LYT4323E3 - POWER INTEGRATIONS

™

LYT4211-4218/4311-4318

LYTSwitch-4 High Power LED Driver IC Family

Single-Stage Accurate Primary-Side Constant Current (CC) Controller with

PFC for Low-Line Applications, TRIAC Dimming and Non-Dimming Options

Part Number Input Voltage Range TRIAC Dimmable

LY T42 21-LY T42 28 160-300 VAC No

LY T4321- LY T4328 160-300 VAC Yes

Output Power Table

Product Minimum Output Power Maximum Output Power

LYT4x21E 6 W 12 W

LYT4x22E 6 W 15 W

LYT4x23E 8 W 18 W

LYT4x24E 9 W 22 W

LYT4x25E 11 W 25 W

LYT4x26E 14 W 35 W

LYT4x27E 19 W 50 W

LYT4x28E 33 W 78 W

Optimized for Different Applications and Power Levels

™

Part Number Input Voltage Range TRIAC Dimmable

LY T4211-LY T4218 85-132 VAC No

LY T4311- LY T4318 85 -132 VAC Yes

Output Power Table

Product Minimum Output Power Maximum Output Power

LYT4x11E/L 2.5 W 12 W

LYT4x12E/L 2.5 W 15 W

LYT4x13E/L 3.8 W 18 W

LYT4x14E/L 4.5 W 22 W

LYT4x15E/L 5.5 W 25 W

LYT4x16E/L 6.8 W 35 W

LYT4x17E/L 8.0 W 50 W

LYT4x18E/L 18 W 78 W

Optimized for Different Applications and Power Levels

Click Here

To read about

LYTSwitch-4 Low-Line

Click Here

To read about

LYTSwitch-4 High-Line

™

LYT4221-4228/4321-4328

LYTSwitch-4 High Power LED Driver IC Family

Single-Stage Accurate Primary-Side Constant Current (CC) Controller with

PFC for High-Line Applications with TRIAC Dimming and Non-Dimming Options

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LYT4211-4218/4311-4318

LYTSwitch-4 High Power LED Driver IC Family

www.powerint.com October 2013

Single-Stage Accurate Primary-Side Constant Current (CC) Controller with

PFC for Low-Line Applications, TRIAC Dimming and Non-Dimming Options

™

Product Highlights

• Better than ±5% CC regulation

• TRIAC dimmable to less than 5% output

• Fast start-up

• <250 ms at full brightness

• <1s at 10% brightness

• High power factor >0.9

• Easily meets EN61000-3-2

• Less than 10% THD in optimized designs

• Up to 92% efﬁcient

• 132 kHz switching frequency for small magnetics

High Performance, Combined Driver, Controller, Switch

The LYTSwitch-4 family enables off-line LED drivers with high

power factor which easily meet international requirements for THD

and harmonics. Output current is tightly regulated with better

than ±5% CC tolerance1. Efﬁciency of up to 92% is easily

achieved in typical applications.

Supports a Wide Selection of TRIAC Dimmers

The LYTSwitch-4 family provides excellent turn-on characteristics

for leading-edge and trailing-edge TRIAC dimming applications.

This results in drivers with a wide dimming range and fast

start-up, even when turning on from a low conduction angle –

large dimming ratio and low “pop-on” current.

Low Solution Cost and Long Lifetime

LYTSwitch-4 ICs are highly integrated and employ a primary-side

control technique that eliminates the optoisolator and reduces

component count. This allows the use of low-cost single-sided

printed circuit boards. Combining PFC and CC functions into a

single-stage also helps reduce cost and increase efﬁciency. The

132 kHz switching frequency permits the use of small, low-cost

magnetics.

LED drivers using the LYTSwitch-4 family do not use primary-

side aluminum electrolytic bulk capacitors. This means greatly

extended driver lifetime, especially in bulb and other high

temperature applications.

Figure 1. Typical Schematic.

PI-6800-050913

LYTSwitch-4

FBR

CONTROL

Part Number Input Voltage Range TRIAC Dimmable

LY T4211-LY T4218 85-132 VAC No

LY T4311- LY T4318 85 -132 VAC Yes

Output Power Table1,2

Product6Minimum Output Power3Maximum Output Power4

LYT4x11E/L52.5 W 12 W

LYT4x12E/L 2.5 W 15 W

LYT4x13E/L 3.8 W 18 W

LYT4x14E/L 4.5 W 22 W

LYT4x15E/L 5.5 W 25 W

LYT4x16E/L 6.8 W 35 W

LYT4x17E/L 8.0 W 50 W

LYT4x18E/L 18 W 78 W

Table 1. Output Power Table.

Notes:

1. Performance for typical design. See Application Note.

2. Continuous power in an open-frame design with adequate heat sinking; device

local ambient of 70 °C. Power level calculated assuming a typical LED string

voltage and efﬁciency >80%.

3. Minimum output power requires CBP = 47 µF.

4. Maximum output power requires CBP = 4.7 µF.

5. LYT4311 CBP = 47 µF, LYT4211 CBP = 4.7 µF.

6. Package: eSIP-7C, eSIP-7F (see Figure 2).

Figure 2. Package Options.

eSIP-7F (L Package) eSIP-7C (E Package)

Optimized for Different Applications and Power Levels

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Figure 3d. Typical Buck-Boost Schematic.

Figure 3c. Typical Tapped-Buck Schematic.

Figure 3b. Typical Buck Schematic.

Figure 3a. Typical Isolated Flyback Schematic.

Table 2. Performance of Different Topologies in a Typical Non-Dimmable 10 W Low-Line Design.

PI-6800-050913

LYTSwitch-4

FBR

CONTROL

Topology Isolation Efﬁciency Cost THD Output Voltage

Isolated Flyback Yes 88% High Best Any

Buck No 92% Low Good Limited

Tapped-Buck No 89% Middle Best Any

Buck-Boost No 90% Low Best High-Voltage

PI-6841-111813

FBR

CONTROL

LYTSwitch-4

PI-6842-111813

CONTROL

IN V

FBR

LYTSwitch-4

Typical Circuit Schematic Key Features

Flyback

Beneﬁts

• Provides isolated output

• Supports widest range of output voltages

• Very good THD performance

Limitations

• Flyback transformer

• Overall efﬁciency reduced by parasitic capacitance

and inductance in the transformer

• Larger PCB area to meet isolation requirements

• Requires additional components (primary clamp and bias)

• Higher RMS switch and winding currents increases losses

and lowers efﬁciency

Buck

Beneﬁts

• Highest efﬁciency

• Lowest component count – small size

• Simple low-cost power inductor

• Low drain source voltage stress

• Best EMI/lowest component count for ﬁlter

Limitations

• Single input line voltage range

• Output voltage <0.6 × VIN(AC) × 1.41

• Output voltage for low THD designs

• Non-isolated

Tapped-Buck

Beneﬁts

• Ideal for low output voltage designs (<20 V)

• High efﬁciency

• Low component count

• Simple low-cost tapped inductor

Limitations

• Designs best suited for single input line voltage

• Requires additional components (primary clamp)

• Non-isolated

Buck-Boost

Beneﬁts

• Ideal for non-isolated high output voltage designs

• High efﬁciency

• Low component count

• Simple common low-cost power inductor can be used

• Lowest THD

Limitations

• Maximum VOUT is limited by MOSFET breakdown voltage

• Single input line voltage range

• Non-isolated

FBR

CONTROL

LYTSwitch-4

PI-6859-111813

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Figure 5. Pin Conﬁguration.

Pin Functional Description

DRAIN (D) Pin:

This pin is the power FET drain connection. It also provides

internal operating current for both start-up and steady-state

operation.

SOURCE (S) Pin:

This pin is the power FET source connection. It is also the

ground reference for the BYPASS, FEEDBACK, REFERENCE

and VOLTAGE MONITOR pins.

BYPASS (BP) Pin:

This is the connection point for an external bypass capacitor for

the internally generated 5.9 V supply. This pin also provides

output power selection through choice of the BYPASS pin

capacitor value.

FEEDBACK (FB) Pin:

The FEEDBACK pin is used for output voltage feedback. The

current into the FEEDBACK pin is directly proportional to the

output voltage. The FEEDBACK pin also includes circuitry to

protect against open load and overload output conditions.

REFERENCE (R) Pin:

This pin is connected to an external precision resistor and is

used to conﬁgure for dimming (LYT4311-4318) and non-TRIAC

dimming (LYT4211-4218) modes of operation.

VOLTAGE MONITOR (V) Pin:

This pin interfaces with an external input line peak detector,

consisting of a rectiﬁer, ﬁlter capacitor and resistors. The

applied current is used to control stop logic for overvoltage (OV),

provide feed-forward to control the output current and the

remote ON/OFF function.

PI-6843-071112

ILIM

DRAIN (D)

SOURCE (S)

BYPASS (BP)

VOLTAGE

MONITOR (V)

FEEDBACK (FB)

REFERENCE (R)

ILIM

VSENSE

5.9 V

5.0 V

BYPASS PIN

UNDERVOLTAGE

FAULT

PRESENT

Gate

Driver

SenseFet

OCP

CURRENT LIMIT

COMPARATOR

1 V

6.4 V

FBOFF

IFB

DCMAX

Comparator

5.9 V

REGULATOR

SOFT-START

TIMER

JITTER

CLOCK

OSCILLATOR

AUTO-RESTART

COUNTER

BYPASS

CAPACITOR

SELECT

FEEDBACK

SENSE

PFC/CC

CONTROL

LINE

SENSE

HYSTERETIC

THERMAL

SHUTDOWN

3-VT

VBG

REFERENCE

BLOCK

LEB

VBG

STOP

LOGIC

PI-5432-082411

Exposed Pad

(backside) Internally

Connected to

SOURCE Pin (see

eSIP-7C Package

Drawing)

1 R

2 V

3 FB

4 BP

5 S

7 D

E Package (eSIP-7C)

(Top View)

Lead Bend Outward

from Drawing

(Refer to eSIP-7F Package

Outline Drawing)

Exposed Pad

(Backside) Internally

Connected to

SOURCE Pin

L Package (eSIP-7F)

Figure 4. Functional Block Diagram.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Functional Description

A LYTSwitch-4 device monolithically combines a controller and

high-voltage power FET into one package. The controller

provides both high power factor and constant current output in

a single-stage. The LYTSwitch-4 controller consists of an

oscillator, feedback (sense and logic) circuit, 5.9 V regulator,

hysteretic over-temperature protection, frequency jittering,

cycle-by-cycle current limit, auto-restart, inductance correction,

power factor and constant current control.

FEEDBACK Pin Current Control Characteristics

The ﬁgure shown below illustrates the operating boundaries of

the FEEDBACK pin current. Above IFB(SKIP) switching is disabled

and below IFB(AR) the device enters into auto-restart.

Figure 6. FEEDBACK Pin Current Characteristic.

The FEEDBACK pin current is also used to clamp the maximum

duty cycle to limit the available output power for overload and

open-loop conditions. This duty cycle reduction characteristic

also promotes a monotonic output current start-up characteristic

and helps preventing over-shoot.

REFERENCE Pin

The REFERENCE pin is tied to ground (SOURCE) via an external

resistor. The value selected sets the internal references,

determining the operating mode for dimming (LYT4311-4318)

and non-dimming (LYT4211-4218) operation and the line

overvoltage thresholds of the VOLTAGE MONITOR pin. For

non-dimming or PWM dimming applications with LYT4211-4218,

the external resistor should be a 24.9 kW ±1%. For phase angle

AC dimming with LYT4311-4318, the external resistor should be

a 49.9 kW ±1%. One percent resistors are recommended as

the resistor tolerance directly affects the output tolerance.

Other resistor values should not be used.

BYPASS Pin Capacitor Power Gain Selection

LYTSwitch-4 devices have the capability to tailor the internal

gain to either full or a reduced output power setting. This allows

selection of a larger device to minimize dissipation for both

thermal and efﬁciency reasons. The power gain is selected with

the value of the BYPASS pin capacitor. The full power setting is

selected with a 4.7 µF capacitor and the reduced power setting

(for higher efﬁciency) is selected with a 47 µF capacitor. The

BYPASS pin capacitor sets both the internal power gain as well

as the over-current protection (OCP) threshold. Unlike the

larger devices, the LYT4x11 power gain is not programmable.

Use a 47 µF capacitor for the LYT4x11.

Switching Frequency

The switching frequency is 132 kHz during normal operation.

To further reduce the EMI level, the switching frequency is

jittered (frequency modulated) by approximately 2.6 kHz.

During start-up the frequency is 66 kHz to reduce start-up time

when the AC input is phase angle dimmed. Jitter is disabled in

deep dimming.

Soft-Start

The controller includes a soft-start timing feature which inhibits

the auto-restart protection feature for the soft-start period (tSOFT)

to distinguish start-up into a fault (short-circuit) from a large

output capacitor. At start-up the LYTSwitch-4 clamps the

maximum duty cycle to reduce the output power. The total

soft-start period is tSOFT.

Remote ON/OFF and EcoSmart™

The VOLTAGE MONITOR pin has a 1 V threshold comparator

connected at its input. This voltage threshold is used for

remote ON/OFF control. When a signal is received at the

VOLTAGE MONITOR pin to disable the output (VOLTAGE

MONITOR pin tied to ground through an optocoupler photo-

transistor) the LYTSwitch-4 will complete its current switching

cycle before the internal power FET is forced off.

The remote ON/OFF feature can also be used as an eco-mode

or power switch to turn off the LYTSwitch-4 and keep it in a

very low power consumption state for indeﬁnite long periods.

When the LYTSwitch-4 is remotely turned on after entering this

mode, it will initiate a normal start-up sequence with soft-start

the next time the BYPASS pin reaches 5.9 V. In the worst case,

the delay from remote on to start-up can be equal to the full

discharge/charge cycle time of the BYPASS pin. This reduced

consumption remote off mode can eliminate expensive and

unreliable in-line mechanical switches.

IFB(AR)

IFB(DCMAXR)

DC10 DCMAX

IFB(SKIP)

IFB

PI-5433-060410

Skip-Cycle

CC Control

Region

Soft-Start and

CC Fold-Back

Region

Auto-Restart

Maximum Duty Cycle

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Figure 7. Remote ON/OFF VOLTAGE MONITOR Pin Control.

5.9 V Regulator/Shunt Voltage Clamp

The internal 5.9 V regulator charges the bypass capacitor

connected to the BYPASS pin to 5.9 V by drawing a current

from the voltage on the DRAIN pin whenever the power FET is

off. The BYPASS pin is the internal supply voltage node. When

the power FET is on, the device operates from the energy stored

in the bypass capacitor. Extremely low power consumption of the

internal circuitry allows LYTSwitch-4 to operate continuously from

current it takes from the DRAIN pin. A bypass capacitor value

of 47 or 4.7 µF is sufﬁcient for both high frequency decoupling

and energy storage. In addition, there is a 6.4 V shunt regulator

clamping the BYPASS pin at 6.4 V when current is provided to

the BYPASS pin through an external resistor. This facilitates

powering of LYTSwitch-4 externally through a bias winding to

increase operating efﬁciency. It is recommended that the

BYPASS pin is supplied current from the bias winding for

normal operation.

Auto-Restart

In the event of an open-loop fault (open FEEDBACK pin resistor

or broken path to feedback winding), output short-circuits or an

overload condition the controller enters into the auto-restart

mode. The controller annunciates both short-circuit and

open-loop conditions once the FEEDBACK pin current falls

below the IFB(AR) threshold after the soft-start period. To minimize

the power dissipation under this fault condition the shutdown/

auto-restart circuit turns the power supply on (same as the

soft-start period) and off at an auto-restart duty cycle of

typically DCAR for as long as the fault condition persists. If the

fault is removed during the auto-restart off-time, the power

supply will remain in auto-restart until the full off-time count is

completed. Special consideration must be made to appropriately

size the output capacitor to ensure that after the soft-start

period (tSOFT) the FEEDBACK pin current is above the IFB(AR)

threshold to ensure successful power-supply start-up. After the

soft-start time period, auto-restart is activated only when the

FEEDBACK pin current falls below IFB(AR).

Over-Current Protection

The current limit circuit senses the current in the power FET.

When this current exceeds the internal threshold (ILIMIT), the power

FET is turned off for the remainder of that cycle. A leading edge

blanking circuit inhibits the current limit comparator for a short

time (tLEB) after the power FET is turned on. This leading edge

blanking time has been set so that current spikes caused by

capacitance and rectiﬁer reverse recovery will not cause

premature termination of the power FET conduction.

Line Overvoltage Protection

This device includes overvoltage detection to limit the maximum

operating voltage detected through the VOLTAGE MONITOR pin.

An external peak detector consisting of a diode and capacitor is

required to provide input line peak voltage to the VOLTAGE

MONITOR pin through a resistor.

The resistor sets line overvoltage (OV) shutdown threshold which,

once exceeded, forces the LYTSwitch-4 to stop switching. Once

the line voltage returns to normal, the device resumes normal

operation. A small amount of hysteresis is provided on the OV

threshold to prevent noise-generated toggling. When the power

FET is off, the rectiﬁed DC high voltage surge capability is

increased to the voltage rating of the power FET (670 V), due to the

absence of the reﬂected voltage and leakage spikes on the drain.

Hysteretic Thermal Shutdown

The thermal shutdown circuitry senses the controller die

temperature. The threshold is set at 142 °C typical with a 75 °C

hysteresis. When the die temperature rises above this threshold

(142 °C) the power FET is disabled and remains disabled until

the die temperature falls by 75 °C, at which point the power FET

is re-enabled.

Safe Operating Area (SOA) Protection

The device also features a safe operating area (SOA) protection

mode which disables FET switching for 40 cycles in the event

the peak switch current reaches the ILIMIT threshold and the switch

on-time is less than tON(SOA). This protection mode protects the

device under short-circuited LED conditions and at start-up during

the soft-start period when auto-restart protection is inhibited.

The SOA protection mode remains active in normal operation.

PI-5435-052510

R FB

CONTROL

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Application Example

20 W TRIAC Dimmable High Power Factor LED Driver

Design Example (DER-350)

The circuit schematic in Figure 8 shows a TRIAC dimmable high

power factor LED driver based on LYT4317E from the LYTSwitch-4

family of devices. The design is conﬁgurable for non-dimmable

only applications by simple component value changes. It was

optimized to drive an LED string at a voltage of 36 V with a

constant current of 0.7 A ideal for Lumens PAR lamp retro-ﬁt

applications. The design operates over an input voltage range

of 90 VAC to 132 VAC.

The key goals of this design were compatibility with standard

leading edge TRIAC AC dimmers, very wide dimming range

(1000:1, 550 mA:0.55 mA), high efﬁciency (>85%) and high

power factor (>0.9). The design is fully protected from faults

such as no-load (open load), overvoltage and output short-

circuit or overload conditions and over temperature.

Circuit Description

The LYTSwitch-4 device (U1- LYT4317E) integrates the power

FET, controller and start-up functions into a single package

reducing the component count versus typical implementations.

Conﬁgured as part of an isolated continuous conduction mode

ﬂyback converter, U1 provides high power factor via its internal

control algorithm together with the small input capacitance of

the design. Continuous conduction mode operation results in

reduced primary peak and RMS current. This both reduces

EMI noise, allowing simpler, smaller EMI ﬁltering components

and improves efﬁciency. Output current regulation is maintained

without the need for secondary-side sensing which eliminates

current sense resistors and improves efﬁciency.

Input Stage

Fuse F1 provides protection from component failures while RV1

provides a clamp during differential line surges, keeping the

peak drain voltage of U1 below the 670 V rating of the internal

power FET. Bridge rectiﬁer BR1 rectiﬁes the AC line voltage.

EMI ﬁltering is provided by L1-L3, C1, C4, R2, R24 and R25

together with the safety rated Y class capacitor (CY1) that bridges

the safety isolation barrier between primary and secondary.

Resistor R2, R24 and R25 act to damp any resonances formed

between L1, L2, L3, C1 and the AC line impedance. A small

bulk capacitor (C4) is required to provide a low impedance

source for the primary switching current. The maximum value

of C2 and C4 is limited in order to maintain a power factor of

greater than 0.9.

LYTSwitch-4 Primary

To provide peak line voltage information to U1 the incoming

rectiﬁed AC peak charges C6 via D2. This is then fed into the

VOLTAGE MONITOR pin of U1 as a current via R10. This

sensed current is also used by the device to set the line input

overvoltage protection threshold. Resistor R9 provides a

discharge path for C6 with a time constant much longer than

that of the rectiﬁed AC to prevent generation of line frequency

ripple.

The VOLTAGE MONITOR pin current and the FEEDBACK pin

current are used internally to control the average output LED

current. For TRIAC phase-dimming applications a 49.9 kW

resistor (R14) is used on the REFERENCE pin and 2 MW (R10)

on the VOLTAGE MONITOR pin to provide a linear relationship

between input voltage and the output current and maximizing

the dimming range.

Diode D3, R15 and C7 clamp the drain voltage to a safe level

due to the effects of leakage inductance. Diode D4 is

necessary to prevent reverse current from ﬂowing through U1

for the period of the rectiﬁed AC input voltage that the voltage

across C4 falls to below the reﬂected output voltage (VOR).

360 kΩ

PI-6875-052213

R FB

CONTROL

FL1

RM8

1 FL2

R10

2 MΩ

R15

200 kΩ

510 kΩ

1/8 W

R24

47 kΩ

1/8 W

510

1/2 W

R25

47 kΩ

1/8 W

47 kΩ

1/8 W

1 mH

R14

49.9 kΩ

1/16 W

R18

165 kΩ

1/16 W

R23

20 kΩ

36 V,

550 mA

90 - 132

VAC

RTN

L N

R19

20 kΩ

1/8 W

100 nF

50 V

R26

30 Ω

R20

39 Ω

1/8 W

R17

3 kΩ

1/10 W

R27

10 Ω

1/10 W

DFLU1400

2.2 nF

630 V

US1J

BAV16

VR4

MAZS3300ML

33 V

MMBT3904

BAV21

X0202MA2BL2

BAV21

BYW29-200

US1D

R22

1 kΩ

1/10 W

BR1

MB6S

600 V

RV1

140 VAC

5 A

C11

330 µF

63 V

C13

100 pF

200 V

CY1

470 pF

250 VAC

C12

330 µF

63 V

47 µF

16 V

C15

100 nF

50 V

C14

10 nF

50 V

56 µF

50 V

LYTSwitch-4

LYT4317E

2.2 µF

250 V

220 nF

250 V

100 nF

250 V

5 mH

100 Ω

1 W

470 nF

50 V

100 nF

250 V

DFLU1400-7

Figure 8. DER-350 Schematic of an Isolated, TRIAC Dimmable, High Power Factor, 90-132 VAC, 20 W / 36 V / 550 mA LED Driver.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Diode D6, C5, C9, R19 and R20 create the primary bias supply

from an auxiliary winding on the transformer. Capacitor C8

provides local decoupling for the BYPASS pin of U1 which is the

supply pin for the internal controller. During start-up C8 is

charged to ~6 V from an internal high-voltage current source

tied to the device DRAIN pin. This allows the part to start

switching at which point the operating supply current is provided

from the bias supply via R17. Capacitor C8 also selects the

output power mode (47 µF for reduced power was selected to

reduce dissipation in U1 and increase efﬁciency for this design).

Feedback

The bias winding voltage is proportional to the output voltage

(set by the turns ratio between the bias and secondary

windings). This allows the output voltage to be monitored

without secondary-side feedback components. Resistor R18

converts the bias voltage into a current which is fed into the

FEEDBACK pin of U1. The internal engine within U1 combines

the FEEDBACK pin current, the VOLTAGE MONITOR pin current

and drain current information to provide a constant output

current over a 1.5:1 output voltage variation (LED string voltage

variation of ±25%) at a ﬁxed line input voltage.

To limit the output voltage at no-load an output overvoltage

protection circuit is set by D8, C15, R22, VR4, R27, C14 and Q2.

Should the output load be disconnected then the bias voltage

will increase until VR4 conducts, turning on Q2 and reducing

the current into the FEEDBACK pin. When this current drops

below 10 µA the part enters auto-restart and switching is

disabled for 300 ms allowing time for the output and bias

voltages to fall.

Output Rectiﬁcation

The transformer secondary winding is rectiﬁed by D7 and

ﬁltered by C11 and C12. An ultrafast TO-220 diode was

selected for efﬁciency and the combined value of C11 and C12

were selected to give peak-to-peak LED ripple current equal to

30% of the mean value. For designs where lower ripple is

desirable the output capacitance value can be increased.

A small pre-load is provided by R23 which discharges residual

charge in output capacitors when turned off.

TRIAC Phase Dimming Control Compatibility

The requirement to provide output dimming with low-cost,

TRIAC-based, leading edge phase dimmers introduces a

number of trade-offs in the design.

Due to the much lower power consumed by LED based lighting

the current drawn by the overall lamp is below the holding

current of the TRIAC within the dimmer. This can cause

undesirable behaviors such as limited dimming range and/or

ﬂickering as the TRIAC ﬁres inconsistently. The relatively large

impedance the LED lamp presents to the line allows signiﬁcant

ringing to occur due to the inrush current charging the input

capacitance when the TRIAC turns on. This too can cause

similar undesirable behavior as the ringing may cause the

TRIAC current to fall to zero and turn off.

To overcome these issues simple two circuits, the SCR active

damper and R-C passive bleeder, are incorporated. The

drawback of these circuits is increased dissipation and

therefore reduced efﬁciency of the supply. For non-dimming

applications these components can simply be omitted.

The SCR active damper consists of components R6, C3, and

Q1 in conjunction with R8. This circuit limits the inrush current

that ﬂows to charge C4 when the TRIAC turns on by placing R8

in series for the ﬁrst ~1 ms of the TRIAC conduction. After

approximately 1 ms, Q1 turns on and bypasses R8. This keeps

the power dissipation on R8 low and allows a larger value

during current limiting. Resistor R6 and C3 provide the delay

on Q1 turn on after the TRIAC conducts. Diode D9 blocks the

charge in capacitor C4 from ﬂowing back after the TRIAC turns

on which helps in dimming compatibility especially with high

power dimmers.

The passive bleeder circuit is comprised of R1 and C1. This

helps keep the input current above the TRIAC holding current

while the input current corresponding to the effective driver

resistance increases during each AC half-cycle.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Modiﬁed DER-350 20 W High Power Factor LED Driver

for Non-Dimmable and Enhanced Line Regulation

The circuit schematic in Figure 9 shows a high power factor

LED driver based on a LYT4317 from the LYTSwitch-4 family of

devices. It was optimized to drive an LED string at a voltage of

36 V with a constant current of 0.55 A, ideal for high lumen PAR

lamp retro-ﬁt applications. The design operates over the

low-line input voltage range of 90 VAC to 132 VAC and is

non-dimming application. A non-dimming application has

tighter output current variation with changes in the line voltage

than a dimming application. It’s key to note that, although not

speciﬁed for dimming, no circuit damage will result if the end

user does operate the design with a phase controlled dimmer.

Modiﬁcation for Non-Dimmable Conﬁguration

The design is conﬁgurable for non-dimmable application by

simply removing the component for SCR active damper (R6,

R8, C3, and Q1), blocking diode D9 and R-C bleeder (R1, C1)

changes and replacing the reference resistor R14 with 24.9 kW.

(See Figure 9)

Key Application Considerations

Power Table

The data sheet power table (Table 1) represents the minimum

and maximum practical continuous output power based on the

following conditions:

• Efﬁciency of 80%

• Device local ambient of 70 °C

• Sufﬁcient heat sinking to keep the device temperature below

100 °C

• For minimum output power column

• Reﬂected output voltage (VOR) of 120 V

• FEEDBACK pin current of 135 µA

• BYPASS pin capacitor value of 47 µF

• For maximum output power column

• Reﬂected output voltage (VOR) of 65 V

• FEEDBACK pin current of 165 µA

• BYPASS pin capacitor value of 4.7 µF (LYT4x11 = 4.7 µF)

Note that input line voltages above 85 VAC do not change the

power delivery capability of LYTSwitch-4 devices.

Device Selection

Select the device size by comparing the required output power

to the values in Table 1. For thermally challenging designs, e.g.,

incandescent lamp replacement, where either the ambient

temperature local to the LYTSwitch-4 device is high and/or

there is minimal space for heat sinking use the minimum output

power column. This is selected by using a 47 µF BYPASS pin

capacitor and results in a lower device current limit and therefore

lower conduction losses. For open frame design or designs

where space is available for heat sinking then refer to the

maximum output power column. This is selected by using a

4.7 µF BYPASS pin capacitor for all but the LYT4x11 which has

only one power setting. In all cases in order to obtain the best

output current tolerance maintain the device temperature below

100 °C

Maximum Input Capacitance

To achieve high power factor, the capacitance used in both the

EMI ﬁlter and for decoupling the rectiﬁed AC (bulk capacitor)

must be limited in value. The maximum value is a function of

the output power of the design and reduces as the output

power reduces. For the majority of designs limit the total

capacitance to less than 200 nF with a bulk capacitor value of

100 nF. Film capacitors are recommended compared to

ceramic types as they minimize audible noise with operating

with leading edge phase dimmers. Start with a value of 10 nF

for the capacitance in the EMI ﬁlter and increase in value until

there is sufﬁcient EMI margin.

PI-6875a-052213

R FB

CONTROL

FL1

RM8

1 FL2

R10

2 MΩ

R15

200 kΩ

510 kΩ

1/8 W

R24

47 kΩ

1/8 W

R25

47 kΩ

1/8 W

47 kΩ

1/8 W

1 mH

R14

24.9 kΩ

1/16 W

R18

165 kΩ

1/16 W

R23

20 kΩ

36 V,

550 mA

90 - 132

VAC

RTN

L N

R19

20 kΩ

1/8 W

100 nF

50 V

R26

30 Ω

R20

39 Ω

1/8 W

R17

3 kΩ

1/10 W

R27

10 Ω

1/10 W

DFLU1400

2.2 nF

630 V

US1J

BAV16

VR4

MAZS3300ML

33 V

MMBT3904

BAV21

BYW29-200

US1D

R22

1 kΩ

1/10 W

BR1

MB6S

600 V

RV1

140 VAC

5 A

C11

330 µF

63 V

C13

100 pF

200 V

CY1

470 pF

250 VAC

C12

330 µF

63 V

47 µF

16 V

C15

100 nF

50 V

C14

10 nF

50 V

56 µF

50 V

LYTSwitch-4

LYT4317E

2.2 µF

250 V

100 nF

250 V

5 mH

100 nF

250 V

Figure 9. Modiﬁed Schematic of RD-350 for Non-Dimmable, Isolated, High Power Factor, 90-132 VAC, 20 W / 36 V LED Driver.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

REFERENCE Pin Resistance Value Selection

The LYTSwitch-4 family contains phase dimming devices,

LYT4311-4318, and non-dimming devices, LYT4211-4218. The

non-dimmable devices use a 24.9 kW ±1% REFERENCE pin

resistor for best output current tolerance (over AC input voltage

changes). The dimmable devices (i.e. LYT4311-4318) use 49.9 kW

±1% to achieve the widest dimming range.

VOLTAGE MONITOR Pin Resistance Network Selection

For widest AC phase angle dimming range with LYT4311-4318,

use a 2 MW (1.7 MW for 100 VAC (Japan)) resistor connected to

the line voltage peak detector circuit. Make sure that the

resistor’s voltage rating is sufﬁcient for the peak line voltage. If

necessary use multiple series connected resistors.

Primary Clamp and Output Reﬂected Voltage VOR

A primary clamp is necessary to limit the peak drain to source

voltage. A Zener clamp requires the fewest components and

board space and gives the highest efﬁciency. RCD clamps are

also acceptable however the peak drain voltage should be

carefully veriﬁed during start-up and output short-circuits as the

clamping voltage varies with signiﬁcantly with the peak drain

current.

For the highest efﬁciency, the clamping voltage should be

selected to be at least 1.5 times the output reﬂected voltage,

VOR, as this keeps the leakage spike conduction time short.

This will ensure efﬁcient operation of the clamp circuit and will

also keep the maximum drain voltage below the rated

breakdown voltage of the FET. An RCD (or RCDZ) clamp

provides tighter clamp voltage tolerance than a Zener clamp.

The RCD clamp is more cost effective than the Zener clamp but

requires more careful design to ensure that the maximum drain

voltage does not exceed the power FET breakdown voltage.

These VOR limits are based on the BVDSS rating of the internal

FET, a VOR of 60 V to 100 V is typical for most designs, giving

the best PFC and regulation performance.

Series Drain Diode

An ultrafast or Schottky diode in series with the drain is

necessary to prevent reverse current ﬂowing through the

device. The voltage rating must exceed the output reﬂected

voltage, VOR. The current rating should exceed two times the

average primary current and have a peak rating equal to the

maximum drain current of the selected LYTSwitch-4 device.

Line Voltage Peak Detector Circuit

LYTSwitch-4 devices use the peak line voltage to regulate the

power delivery to the output. A capacitor value of 1 µF to 4.7 µF

is recommended to minimize line ripple and give the highest

power factor (>0.9), smaller values are acceptable but result in

lower PF and higher line current distortion.

Operation with Phase Controlled Dimmers

Dimmer switches control incandescent lamp brightness by not

conducting (blanking) for a portion of the AC voltage sine wave.

This reduces the RMS voltage applied to the lamp thus reducing

the brightness. This is called natural dimming and the LYTSwitch-4

LYT4311-4318 devices when conﬁgured for dimming utilize

natural dimming by reducing the LED current as the RMS line

voltage decreases. By this nature, line regulation performance is

purposely decreased to increase the dimming range and more

closely mimic the operation of an incandescent lamp. Using a

49.9 kW REFERENCE pin resistance selects natural dimming

mode operation.

Leading Edge Phase Controlled Dimmers

The requirement to provide ﬂicker-free output dimming with low-

cost, TRIAC-based, leading edge phase dimmers introduces a

number of trade-offs in the design.

Due to the much lower power consumed by LED based lighting

the current drawn by the overall lamp is below the holding

current of the TRIAC within the dimmer. This causes

undesirable behaviors such as limited dimming range and/or

ﬂickering. The relatively large impedance the LED lamp presents

to the line allows signiﬁcant ringing to occur due to the inrush

current charging the input capacitance when the TRIAC turns

on. This too can cause similar undesirable behavior as the

ringing may cause the TRIAC current to fall to zero and turn off.

To overcome these issues two circuits, the active damper and

passive bleeder, are incorporated. The drawback of these

circuits is increased dissipation and therefore reduced efﬁciency

of the supply so for non-dimming applications these components

can simply be omitted.

Figure 10a shows the line voltage and current at the input of a

leading edge TRIAC dimmer with Figure 10b showing the

resultant rectiﬁed bus voltage. In this example, the TRIAC

conducts at 90 degrees.

50 100 150 200 250 300 350 400

Conduction Angle (°)

Line Voltage (at Dimmer Input) (V)

Line Current (Through Dimmer) (A)

350

250

150

-50

-150

-250

-350

0.35

0.25

0.15

0.05

-0.05

-0.15

-0.25

-0.35

PI-5983-060810

Voltage

Current

0.5

Figure 10a. Ideal Input Voltage and Current Waveform for a Leading Edge

TRIAC Dimmer at 90°.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

050 100 150 200 250 400350300

Conduction Angle (°)

Rectified Input Voltage (V)

Rectified Input Current (A)

350

300

250

200

150

100

0.35

0.3

0.25

0.2

0.15

0.1

0.05

PI-5984-060810

Voltage

Current

Figure 10b. Resultant Waveforms Following Rectiﬁcation of TRIAC Dimmer Output.Figure 12. Ideal Dimmer Output Voltage and Current Waveforms for a Trailing

Edge Dimmer at 90° Conduction Angle.

Figure 11. Example of Phase Angle Dimmer Showing Erratic Firing.

Figure 11 shows undesired rectiﬁed bus voltage and current

with the TRIAC turning off prematurely and restarting.

If the TRIAC is turning off before the end of the half-cycle

erratically or alternate half AC cycles have different conduction

angles then ﬂicker will be observed in the LED light due to

variations in the output current. This can be solved by including

a bleeder and damper circuit.

Dimmers will behave differently based on manufacturer and

power rating, for example a 300 W dimmer requires less

dampening and requires less power loss in the bleeder than a

600 W or 1000 W dimmer due to different drive circuits and

TRIAC holding current speciﬁcations. Multiple lamps in parallel

driven from the same dimmer can introduce more ringing due to

the increased capacitance of parallel units. Therefore, when

testing dimmer operation verify on a number of models,

different line voltages and with both a single driver and multiple

drivers in parallel.

Start by adding a bleeder circuit. Add a 0.44 µF capacitor and

510 W 1 W resistor (components in series) across the rectiﬁed

bus (C1 and R1 in Figure 8). If the results in satisfactory operation

reduce the capacitor value to the smallest that result in acceptable

performance to reduce losses and increase efﬁciency.

If the bleeder circuit does not maintain conduction in the TRIAC,

then add an active damper as shown in Figure 8. This consists

of components R6, C3, and Q1 in conjunction with R8. This

circuit limits the inrush current that ﬂows to charge C4 when the

TRIAC turns on by placing R8 in series for the ﬁrst 1 ms of the

TRIAC conduction. After approximately 1 ms, Q1 turns on and

shorts R8. This keeps the power dissipation on R8 low and

allows a larger value to be used during current limiting.

Increasing the delay before Q1 turns on by increasing the value

of resistor R6 will improve dimmer compatibility but cause more

power to be dissipated across R8. Monitor the AC line current

and voltage at the input of the power supply as you make the

adjustments. Increase the delay until the TRIAC operates

properly but keep the delay as short as possible for efﬁciency.

As a general rule the greater the power dissipated in the bleeder

and damper circuits, the more types of dimmers will work with

the driver.

Trailing Edge Phase Controlled Dimmers

Figure 11 shows the line voltage and current at the input of the

power supply with a trailing edge dimmer. In this example, the

dimmer conducts at 90 degrees. Many of these dimmers use

back-to-back connected power FETs rather than a TRIAC to

control the load. This eliminates the holding current issue of

TRIACs and since the conduction begins at the zero crossing,

high current surges and line ringing are minimized. Typically these

types of dimmers do not require damping and bleeder circuits.

050 100 150 200 250 400350300

Conduction Angle (°)

Rectiﬁed Input Voltage (V)

Rectiﬁed Input Current (A)

350

300

250

200

150

100

0.35

0.3

0.25

0.2

0.15

0.1

0.05

PI-5985-060810

Voltage

Current

50 100 150 200 250 300 350

Conduction Angle (°)

Dimmer Output Voltage (V)

Dimmer Output Current (A)

350

250

150

-50

-150

-250

-350

0.35

0.25

0.15

0.05

-0.05

-0.15

-0.25

-0.35

PI-5986-060810

Voltage

Current

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Audible Noise Considerations for Use with

Leading Edge Dimmers

Noise created when dimming is typically created by the input

capacitors, EMI ﬁlter inductors and the transformer. The input

capacitors and inductors experience high di/dt and dv/dt every

AC half-cycle as the TRIAC ﬁres and an inrush current ﬂows to

charge the input capacitance. Noise can be minimized by

selecting ﬁlm vs. ceramic capacitors, minimizing the capacitor

value and selecting inductors that are physically short and wide.

The transformer may also create noise which can be minimized

by avoiding cores with long narrow legs (high mechanical

resonant frequency). For example, RM cores produce less

audible noise than EE cores for the same ﬂux density. Reducing

the core ﬂux density will also reduce the noise. Reducing the

maximum ﬂux density (BM) to 1500 Gauss usually eliminates

any audible noise but must be balanced with the increased core

size needed for a given output power.

Thermal and Lifetime Considerations

Lighting applications present thermal challenges to the driver.

In many cases the LED load dissipation determines the working

ambient temperature experienced by the drive so thermal

evaluation should be performed with the driver inside the ﬁnal

enclosure. Temperature has a direct impact on driver and LED

lifetime. For every 10 °C rise in temperature, component life is

reduced by a factor of 2. Therefore it is important to properly

heat sink and to verify the operating temperatures of all devices.

Layout Considerations

Primary-Side Connections

Use a single point (Kelvin) connection at the negative terminal of

the input ﬁlter capacitor for the SOURCE pin and bias returns.

This improves surge capabilities by returning surge currents

from the bias winding directly to the input ﬁlter capacitor. The

BYPASS pin capacitor should be located as close to the

BYPASS pin and connected as close to the SOURCE pin as

possible. The SOURCE pin trace should not be shared with the

main power FET switching currents. All FEEDBACK pin

components that connect to the SOURCE pin should follow the

same rules as the BYPASS pin capacitor. It is critical that the

main power FET switching currents return to the bulk capacitor

with the shortest path as possible. Long high current paths

create excessive conducted and radiated noise.

Secondary-Side Connections

The output rectiﬁer and output ﬁlter capacitor should be as

close as possible. The transformer’s output return pin should

have a short trace to the return side of the output ﬁlter capacitor.

Figure 13. DER-350 20 W Layout Example, Top Silk / Bottom Layer.

PI-6904-072313

Output

Capacitors

VOLTAGE MONITOR Pin

Resistor

FEEDBACK Pin

Resistor

REFERENCE Pin

Resistor

Input EMI Filter

LYT4317E

Bullk

Capacitor

Clamp Transformer Output

Diode

Output

Capacitor

BYPASS Pin

Capacitor

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Quick Design Checklist

Maximum Drain Voltage

Verify that the peak VDS does not exceed 670 V under all

operating conditions including start-up and fault conditions.

Maximum Drain Current

Measure the peak drain current under all operation conditions

including start-up and fault conditions. Look for signs of

transformer saturation (usually occurs at highest operating

ambient temperatures). Verify that the peak current is less than

the stated Absolute Maximum Rating in the data sheet.

Thermal Check

At maximum output power, both minimum and maximum line

voltage and ambient temperature; verify that temperature

speciﬁcations are not exceeded for the LYTSwitch-4,

transformer, output diodes, output capacitors and drain clamp

components.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Parameter Symbol

Conditions

SOURCE = 0 V; TJ = -20 °C to 125 °C

(Unless Otherwise Speciﬁed)

Min Typ Max Units

Control Functions

Switching Frequency fOSC TJ = 65 °C

Average 124 132 140

kHz

Peak-Peak Jitter 5.4

Frequency Jitter

Modulation Rate fM

TJ = 65 °C

See Note B 2.6 kHz

BYPASS Pin

Charge Current

ICH1

VBP = 0 V,

TJ = 65 °C

LYT4x11 -4.1 -3.4 -2.7

LYT4x12 -7.3 -6.1 -4.9

LYT4x13-4x17 -12 -9.5 -7.0

LYT4x18 -13.3 -10.8 -8.3

ICH2

VBP = 5 V,

TJ = 65 °C

LYT4x11 -0.81 -0.62 -0.43

LYT4x12 -3.1 -2.4 -1.7

LYT4x13-4x17 -5.6 -4.35 -3.1

LYT4x18 -6.75 -5.5 -4.25

Charging Current

Temperature Drift See Note A, B 0.7 %/°C

BYPASS Pin Voltage VBP 0 °C < TJ < 100 °C 5.75 5.95 6.15 V

BYPASS Pin

Voltage Hysteresis VBP(H) 0 °C < TJ < 100 °C 0.85 V

BYPASS Pin

Shunt Voltage VBP(SHUNT)

IBP = 4 mA

0 °C < TJ < 100 °C 6.1 6.4 6.6 V

Soft-Start Time tSOFT

TJ = 65 °C

VBP = 5.9 V 55 76 ms

Absolute Maximum Ratings(1,4)

DRAIN Pin Peak Current(5): LY T4x11 .................................1.37 A

LY T4x12 .................................2.08 A

LY T4x13 .................................2.72 A

LY T4x14 ................................ 4.08 A

LY T4x15 ................................ 5.44 A

LY T4x16 ................................ 6.88 A

LY T4x17 ................................. 7.7 3 A

LY T4x18 ................................ 9.00 A

DRAIN Pin Voltage ……………………… ................. -0.3 to 670 V

BYPASS Pin Voltage ................................................. -0.3 to 9 V

BYPASS Pin Current ……………………… ...................... 100 mA

VOLTAGE MONITOR Pin Voltage .............................-0.3 to 9 V(6)

FEEDBACK Pin Voltage …….. .................................. -0.3 to 9 V

REFERENCE Pin Voltage .......................................... -0.3 to 9 V

Lead Temperature(3) ........................................................260 °C

Storage Temperature …………………. .................. -65 to 150 °C

Operating Junction Temperature(2) .........................-40 to 150 °C

Notes:

1. All voltages referenced to SOURCE, TA = 65 °C.

2. Normally limited by internal circuitry.

3. 1/16 in. from case for 5 seconds.

4. Absolute Maximum Ratings speciﬁed may be applied, one

at a time without causing permanent damage to the

product. Exposure to Absolute Maximum Ratings for

extended periods of time may affect product reliability.

5. Peak DRAIN current is allowed while the DRAIN voltage is

simultaneously less than 400 V. See also Figure 13.

6. During start-up (the period before the BYPASS pin begins

powering the IC) the VOLTAGE MONITOR pin voltage can

safely rise to 15 V without damage.

Thermal Resistance

Thermal Resistance: E or L Package

(qJA) ....................................................105 °C/W(1)

(qJC) .................................................... 2 °C/W(2)

Notes:

1. Free standing with no heat sink.

2. Measured at back surface tab.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Parameter Symbol

Conditions

SOURCE = 0 V; TJ = -20 °C to 125 °C

(Unless Otherwise Speciﬁed)

Min Typ Max Units

Control Functions (cont.)

Drain Supply Current

ICD2

0 °C < TJ < 100 °C

FET Not Switching 0.5 0.8 1.2

ICD1

0 °C < TJ < 100 °C

FET Switching at fOSC

1 2.5 4

VOLTAGE MONITOR Pin

Line Overvoltage

Threshold IOV

TJ = 65 °C

RR = 24.9 kW

RR = 49.9 kW

Threshold 115 123 131

µA

Hysteresis 6

VOLTAGE MONITOR

Pin Voltage VV

0 °C < TJ < 100 °C

IV < IOV

2.75 3.0 3.25 V

VOLTAGE MONITOR Pin

Short-Circuit Current IV(SC)

VV = 5 V

TJ = 65 °C 165 185 205 µA

Remote ON/OFF

Threshold VV(REM) TJ = 65 °C 0.5 V

FEEDBACK Pin

FEEDBACK Pin Current

at Onset of Maximum

Duty Cycle

IFB(DCMAXR) 0 °C < TJ < 100 °C 90 µA

FEEDBACK Pin Current

Skip Cycle Threshold IFB(SKIP) 0 °C < TJ < 100 °C 210 µA

Maximum Duty Cycle DCMAX

IFB(DCMAXR) < IFB < IFB(SKIP)

0 °C < TJ < 100 °C 90 99.9 %

FEEDBACK Pin Voltage VFB

IFB = 150 µA

0 °C < TJ < 100 °C 2.1 2.3 2.56 V

FEEDBACK Pin

Short-Circuit Current IFB(SC)

VFB = 5 V

TJ = 65 °C 320 400 480 µA

Duty Cycle Reduction

DC10 IFB = IFB(AR), TJ = 65 °C, See Note B 17

%DC40 IFB = 40 µA, TJ = 65 °C 34

DC60 IFB = 60 µA, TJ = 65 °C 55

Auto-Restart

Auto-Restart ON-Time tAR

TJ = 65 °C

VBP = 5.9 V 55 76 ms

Auto-Restart

Duty Cycle DCAR

TJ = 65 °C

See Note B 25 %

SOA Minimum Switch

ON-Time tON(SOA)

TJ = 65 °C

See Note B 0.875 µs

FEEDBACK Pin Current

During Auto-Restart IFB(AR) 0 °C < TJ < 100 °C 6.5 10 µA

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Parameter Symbol

Conditions

SOURCE = 0 V; TJ = -20 °C to 125 °C

(Unless Otherwise Speciﬁed)

Min Typ Max Units

REFERENCE Pin

Voltage VRRR = 24.9 kW

0 °C < TJ < 100 °C

1.223 1.245 1.273 V

REFERENCE Pin

Current IR48.69 49.94 51.19 µA

Current Limit/Circuit Protection

Full Power

Current Limit

(CBP = 4.7 µF)

ILIMIT(F)

TJ = 65 °C

di/dt = 174 mA/µs LYT4x12 1.00 1.17

di/dt = 174 mA/µs LYT4x13 1.24 1.44

di/dt = 225 mA/µs LYT4x14 1.46 1.70

di/dt = 320 mA/µs LYT4x15 1.76 2.04

di/dt = 350 mA/µs LYT4x16 2.43 2.83

di/dt = 426 mA/µs LYT4x17 3.26 3.79

Reduced Power

Current Limit

(CBP = 47 µF)

ILIMIT(R)

TJ = 65 °C

di/dt = 133 mA/µs LYT4x11 0.74 0.86

di/dt = 195 mA/µs LYT4x12 0.81 0.95

di/dt = 192 mA/µs LYT4x13 1.00 1.16

di/dt = 240 mA/µs LYT4x14 1.19 1.38

di/dt = 335 mA/µs LYT4x15 1.43 1.66

di/dt = 380 mA/µs LYT4x16 1.76 2.05

di/dt = 483 mA/µs LYT4x17 2.35 2.73

di/dt = 930 mA/µs LYT4x18 4.90 5.70

Minimum ON-Time

Pulse tLEB + tIL(D) TJ = 65 °C 300 500 700 ns

Leading Edge

Blanking Time tLEB

TJ = 65 °C

See Note B 150 500 ns

Current Limit Delay tIL(D)

TJ = 65 °C

See Note B 150 ns

Thermal Shutdown

Temperature See Note B 135 142 150 °C

Thermal Shutdown

Hysteresis See Note B 75 °C

BYPASS Pin Power-Up

Reset Threshold

Voltage

VBP(RESET) 0 °C < TJ < 100 °C 2.25 3.30 4.25 V

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Parameter Symbol

Conditions

SOURCE = 0 V; TJ = -20 °C to 125 °C

(Unless Otherwise Speciﬁed)

Min Typ Max Units

Output

ON-State Resistance RDS(ON)

LYT4x11

ID = 100 mA

TJ = 65 °C 11.5 13.2

TJ = 100 °C 13.5 15.5

LYT4x12

ID = 100 mA

TJ = 65 °C 6.9 8.0

TJ = 100 °C 8.4 9.7

LYT4x13

ID = 150 mA

TJ = 65 °C 5.3 6.0

TJ = 100 °C 6.3 7.3

LYT4x14

ID = 150 mA

TJ = 65 °C 3.4 3.9

TJ = 100 °C 3.9 4.5

LYT4x15

ID = 200 mA

TJ = 65 °C 2.5 2.9

TJ = 100 °C 3.0 3.4

LYT4x16

ID = 250 mA

TJ = 65 °C 1.9 2.2

TJ = 100 °C 2.3 2.7

LYT4x17

ID = 350 mA

TJ = 65 °C 1.7 2.0

TJ = 100 °C 2.0 2.4

LYT4x18

ID = 600 mA

TJ = 65 °C 1.3 1.5

TJ = 100 °C 1.6 1.8

OFF-State Drain

Leakage Current IDSS

VBP = 6.4 V

VDS = 560 V

TJ = 100 °C

50 µA

Breakdown Voltage BVDSS

VBP = 6.4 V

TJ = 65 °C 670 V

Minimum Drain

Supply Voltage TJ < 100 °C 36 V

Rise Time tRMeasured in a Typical Flyback

See Note B

100 ns

Fall Time tF50 ns

NOTES:

A. For speciﬁcations with negative values, a negative temperature coefﬁcient corresponds to an increase in magnitude with increasing

temperature and a positive temperature coefﬁcient corresponds to a decrease in magnitude with increasing temperature.

B. Guaranteed by characterization. Not tested in production.

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Typical Performance Characteristics

Figure 14. Drain Capacitance vs. Drain Pin Voltage. Figure 15. Power vs. Drain Voltage.

Figure 16. Drain Current vs. Drain Voltage. Figure 17. Maximum Allowable Drain Current vs. Drain Voltage.

1 100 200 300 400 500 600

100

1000

10000

PI-6715-072313

DRAIN Pin Voltage (V)

DRAIN Capacitance (pF)

LYT4x11 0.18

LYT4x12 0.28

LYT4x13 0.38

LYT4x14 0.56

LYT4x15 0.75

LYT4x16 1.00

LYT4x17 1.16

LYT4x18 1.55

Scaling Factors:

300

100

200

0 200100 400 500 600300 700

DRAIN Voltage (V)

Power (mW)

PI-6716-071012

LYT4x11 0.18

LYT4x12 0.28

LYT4x13 0.38

LYT4x14 0.56

LYT4x15 0.75

LYT4x16 1.00

LYT4x17 1.16

LYT4x18 1.55

Scaling Factors:

02 4 6 8 10 12 14 16 18 20

DRAIN Voltage (V)

DRAIN Current (A)

PI-6717-071012

LYT4x28 TCASE = 25 °C

LYT4x28 TCASE = 100 °C

LYT4x11 0.18

LYT4x12 0.28

LYT4x13 0.38

LYT4x14 0.56

LYT4x15 0.75

LYT4x16 1.00

LYT4x17 1.16

LYT4x18 1.55

Scaling Factors:

0100 200 300 400 600500 700 800

DRAIN Voltage (V)

DRAIN Current

(Normalized to Absolute Maximum Rating)

PI-6909-110512

0.6

0.8

0.4

0.2

1.2

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

PI-4917-061510

MOUNTING HOLE PATTERN

(not to scale)

PIN 7

PIN 1

0.100 (2.54) 0.100 (2.54)

0.059 (1.50)

0.050 (1.27)

0.100 (2.54)

0.155 (3.93)

0.020 (0.50)

Notes:

1. Dimensioning and tolerancing per ASME Y14.5M-1994.

2. Dimensions noted are determined at the outermost

extremes of the plastic body exclusive of mold ﬂash,

tie bar burrs, gate burrs, and interlead ﬂash, but including

any mismatch between the top and bottom of the plastic

body. Maximum mold protrusion is 0.007 [0.18] per side.

3. Dimensions noted are inclusive of plating thickness.

4. Does not include inter-lead ﬂash or protrusions.

5. Controlling dimensions in inches (mm).

0.403 (10.24)

0.397 (10.08)

0.325 (8.25)

0.320 (8.13)

0.050 (1.27)

FRONT VIEW

0.070 (1.78) Ref.

Pin #1

I.D.

0.016 (0.41)

Ref.

0.290 (7.37)

Ref.

0.047 (1.19)

0.100 (2.54)

0.519 (13.18)

Ref.

0.198 (5.04) Ref.

0.264 (6.70)

Ref.

0.118 (3.00)

6×

0.140 (3.56)

0.120 (3.05)

0.021 (0.53)

0.019 (0.48)

0.378 (9.60)

Ref. 0.019 (0.48) Ref.

0.060 (1.52)

Ref.

0.048 (1.22)

0.046 (1.17)

0.081 (2.06)

0.077 (1.96)

0.207 (5.26)

0.187 (4.75)

0.033 (0.84)

0.028 (0.71)

0.016 (0.41)

0.011 (0.28)

eSIP-7C (E Package)

10° Ref.

All Around

0.020 M 0.51 M C

0.010 M 0.25 M C A B

SIDE VIEW

END VIEW

BACK VIEW

0.023 (0.58)

0.027 (0.70)

DETAIL A

Detail A

Rev. D 10/13

LYT4211-4218/4311-4318

www.powerint.com

Part Ordering Information

• LYTSwitch-4 Product Family

• 4 Series Number

• PFC/Dimming

2 PFC No Dimming

3 PFC Dimming

• Voltage Range

1 Low-Line

• Device Size

• Package Identiﬁer

E eSIP-7C

L eSIP-7F

LYT 4 2 1 3 E

1 7

END VIEW

0.021 (0.53)

0.019 (0.48)

0.060 (1.52) Ref.

0.019 (0.48) Ref. 0.378 (9.60)

Ref.

0.048 (1.22)

0.046 (1.17)

SIDE VIEW

6×

0.129 (3.28)

0.122 (3.08)

0.081 (2.06)

0.077 (1.96)

Detail A

0.084 (2.14)

0.047 (1.19) Ref.

0.290 (7.37)

Ref.

0.016 (0.41)

0.011 (0.28)

0.020 M 0.51 M C

PI-5204-061510

Notes:

1. Dimensioning and tolerancing per ASME

Y14.5M-1994.

2. Dimensions noted are determined at the

outermost extremes of the plastic body

exclusive of mold ﬂash, tie bar burrs, gate

burrs, and interlead ﬂash, but including

any mismatch between the top and bottom

of the plastic body. Maximum mold

protrusion is 0.007 [0.18] per side.

3. Dimensions noted are inclusive of plating

thickness.

4. Does not include inter-lead ﬂash or

protrusions.

5. Controlling dimensions in inches (mm).

eSIP-7F (L Package)

1 7

BOTTOM VIEW

Pin 1 I.D.

0.403 (10.24)

0.397 (10.08)

0.325 (8.25)

0.320 (8.13)

0.050 (1.27)

0.070 (1.78) Ref.

Exposed pad hidden Exposed pad up

TOP VIEW

0.089 (2.26)

0.079 (2.01)

0.173 (4.40)

0.163 (4.15)

0.198 (5.04) Ref.

0.264 (6.70) Ref.

0.100 (2.54)

0.490 (12.45) Ref.

6×

0.033 (0.84)

0.028 (0.71)

0.010 M 0.25 M C A B

0.020 (0.50)

0.023 (0.58)

0.027 (0.70)

DETAIL A (Not drawn to scale)

For the latest updates, visit our website: www.powerint.com

Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power

Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES

NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED

WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS.

Patent Information

The products and applications illustrated herein (including transformer construction and circuits external to the products) may be covered

by one or more U.S. and foreign patents, or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A

complete list of Power Integrations patents may be found at www.powerint.com. Power Integrations grants its customers a license under

certain patent rights as set forth at http://www.powerint.com/ip.htm.

Life Support Policy

POWER INTEGRATIONS PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR

SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF POWER INTEGRATIONS. As used herein:

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whose failure to perform, when properly used in accordance with instructions for use, can be reasonably expected to result in signiﬁcant

injury or death to the user.

2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause

the failure of the life support device or system, or to affect its safety or effectiveness.

The PI logo, TOPSwitch, TinySwitch, LinkSwitch, LYTSwitch, DPA-Switch, PeakSwitch, CAPZero, SENZero, LinkZero, HiperPFS, HiperTFS,

HiperLCS, Qspeed, EcoSmart, Clampless, E-Shield, Filterfuse, StakFET, PI Expert and PI FACTS are trademarks of Power Integrations, Inc.

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Revision Notes Date

A Initial Release. 11/12

B Corrected Min and Typ parameter table values on pages 13 and 14. 02/13

B Updated parameters ICH1, ICH2, ICD1, DCAR, ILIMIT(F), ILIMIT(R), on pages 13, 14 and 15. 02/20/13

C Updated ﬁgures 1, 3a, 3b, 3c, 3d, 8, 9 and 13. 06/13

D Added Note 6 to Absolute Maximum Ratings section. 10/13

LYT4221-4228/4321-4328

LYTSwitch-4 High Power LED Driver IC Family

www.powerint.com March 2014

Single-Stage Accurate Primary-Side Constant Current (CC) Controller with

PFC for High-Line Applications with TRIAC Dimming and Non-Dimming Options

™

This Product is Covered by Patents and/or Pending Patent Applications.

Product Highlights

• Better than ±5% CC regulation

• TRIAC dimmable to less than 5% output

• Fast start-up

• <250 ms at full brightness

• <1s at 10% brightness

• High power factor >0.9

• Easily meets EN61000-3-2

• Less than 10% THD in optimized designs

• Up to 92% efﬁcient

• 132 kHz switching frequency for small magnetics

High Performance, Combined Driver, Controller, Switch

The LYTSwitch family enables off-line LED drivers with high

power factor which easily meet international requirements for

THD and harmonics. Output current is tightly regulated with

better than ±5% CC tolerance1. Efﬁciency of up to 92% is easily

achieved in typical applications.

Supports a Wide Selection of TRIAC Dimmers

The LYTSwitch family provides excellent turn-on characteristics

for leading-edge and trailing-edge TRIAC dimming applications.

This results in drivers with a wide dimming range and fast

start-up, even when turning on from a low conduction angle –

large dimming ratio and low “pop-on” current.

Low Solution Cost and Long Lifetime

LYTSwitch ICs are highly integrated and employ a primary-side

control technique that eliminates the optoisolator and reduces

component count. This allows the use of low-cost single-sided

printed circuit boards. Combining PFC and CC functions into a

single-stage also helps reduce cost and increase efﬁciency.

The 132 kHz switching frequency permits the use of small,

low-cost magnetics.

LED drivers using the LYTSwitch family do not use primary-side

aluminum electrolytic bulk capacitors. This means greatly

extended driver lifetime, especially in bulb and other high

temperature applications.

Figure 1. Typical Schematic.

PI-6800-050913

LYTSwitch-4

FBR

CONTROL

Part Number Input Voltage Range TRIAC Dimmable

LY T42 21-LY T42 28 160-300 VAC No

LY T4321- LY T4328 160-300 VAC Yes

Output Power Table1,2

Product6Minimum Output Power3Maximum Output Power4

LYT4x21E56 W 12 W

LYT4x22E 6 W 15 W

LYT4x23E 8 W 18 W

LYT4x24E 9 W 22 W

LYT4x25E 11 W 25 W

LYT4x26E 14 W 35 W

LYT4x27E 19 W 50 W

LYT4x28E 33 W 78 W

Table 1. Output Power Table.

Notes:

1. Performance for typical design. See Application Note.

2. Continuous power in an open frame design with adequate heat sinking; device

local ambient of 70 °C. Power level calculated assuming a typical LED string

voltage and efﬁciency >80%.

3. Minimum output power requires CBP = 47 µF.

4. Maximum output power requires CBP = 4.7 µF.

5. LYT4321 CBP = 47 µF, LYT4221 CBP = 4.7 µF.

6. Package: eSIP-7C (see Figure 2).

Figure 2. Package Options.

eSIP-7C (E Package)

Optimized for Different Applications and Power Levels

Rev. B 03/14

LYT4221-4228/4321-4328

www.powerint.com

Figure 3d. Typical Buck-Boost Schematic.

Figure 3c. Typical Tapped Buck Schematic.

Figure 3b. Typical Buck Schematic.

Figure 3a. Typical Isolated Flyback Schematic.

Table 2. Performance of Different Topologies in a Typical Non-Dimmable 10 W High-Line Design.

PI-6800-050913

LYTSwitch-4

FBR

CONTROL

Topology Isolation Efﬁciency Cost THD Output Voltage

Isolated Flyback Yes 88% High Best Any

Buck No 92% Low Good Limited

Tapped Buck No 89% Middle Best Any

Buck-Boost No 90% Low Best High-Voltage

Typical Circuit Schematic Key Features

Flyback

Beneﬁts

• Provides isolated output

• Supports widest range of output voltages

• Very good THD performance

Limitations

• Flyback transformer

• Overall efﬁciency reduced by parasitic capacitance

and inductance in the transformer

• Larger PCB area to meet isolation requirements

• Requires additional components (primary clamp and bias)

• Higher RMS switch and winding currents increases losses

and lowers efﬁciency

Buck

Beneﬁts

• Highest efﬁciency

• Lowest component count – small size

• Simple low-cost power inductor

• Low drain source voltage stress

• Best EMI/lowest component count for ﬁlter

Limitations

• Single input line voltage range

• Output voltage <0.6 × VIN(AC) × 1.41

• Output voltage for low THD designs

• Non-isolated

Tapped Buck

Beneﬁts

• Ideal for low output voltage designs (<20 V)

• High efﬁciency

• Low component count

• Simple low-cost tapped inductor

Limitations

• Designs best suited for single input line voltage

• Requires additional components (primary clamp)

• Non-isolated

Buck-Boost

Beneﬁts

• Ideal for non-isolated high output voltage designs

• High efﬁciency

• Low component count

• Simple common low-cost power inductor can be used

• Lowest THD

Limitations

• Maximum VOUT is limited by MOSFET breakdown voltage

• Single input line voltage range

• Non-isolated

PI-6841-111813

FBR

CONTROL

LYTSwitch-4

PI-6842-111813

CONTROL

IN V

FBR

LYTSwitch-4

FBR

CONTROL

LYTSwitch-4

PI-6859-111813

Rev. B 03/14

LYT4221-4228/4321-4328

www.powerint.com

Figure 5. Pin Conﬁguration.

Pin Functional Description

DRAIN (D) Pin:

This pin is the power FET drain connection. It also provides

internal operating current for both start-up and steady-state

operation.

SOURCE (S) Pin:

This pin is the power FET source connection. It is also the

ground reference for the BYPASS, FEEDBACK, REFERENCE

and VOLTAGE MONITOR pins.

BYPASS (BP) Pin:

This is the connection point for an external bypass capacitor for

the internally generated 5.9 V supply. This pin also provides

output power selection through choice of the BYPASS pin

capacitor value.

FEEDBACK (FB) Pin:

The FEEDBACK pin is used for output voltage feedback. The

current into the FEEDBACK pin is directly proportional to the

output voltage. The FEEDBACK pin also includes circuitry to

protect against open load and overload output conditions.

REFERENCE (R) Pin:

This pin is connected to an external precision resistor and is

conﬁgured to use only 24.9 kW for non-dimming and dimming.

VOLTAGE MONITOR (V) Pin:

This pin interfaces with an external input line peak detector,

consisting of a rectiﬁer, ﬁlter capacitor and resistors. The

applied current is used to control stop logic for overvoltage (OV),

provide feed-forward to control the output current and the

remote ON/OFF function.

PI-6843-071112

ILIM

DRAIN (D)

SOURCE (S)

BYPASS (BP)

VOLTAGE

MONITOR (V)

FEEDBACK (FB)

REFERENCE (R)

ILIM

VSENSE

5.9 V

5.0 V

BYPASS PIN

UNDERVOLTAGE

FAULT

PRESENT

Gate

Driver

SenseFet

OCP

CURRENT LIMIT

COMPARATOR

1 V

6.4 V

FBOFF

IFB

DCMAX

Comparator

5.9 V

REGULATOR

SOFT-START

TIMER

JITTER

CLOCK

OSCILLATOR

AUTO-RESTART

COUNTER

BYPASS

CAPACITOR

SELECT

FEEDBACK

SENSE

PFC/CC

CONTROL

LINE

SENSE

HYSTERETIC

THERMAL

SHUTDOWN

3-VT

VBG

REFERENCE

BLOCK

LEB

VBG

STOP

LOGIC

PI-7076-062513

Exposed Pad

(Backside) Internally

Connected to

SOURCE Pin (see

eSIP-7C Package

Drawing)

E Package (eSIP-7C)

(Top View)

1 R

2 V

3 FB

4 BP

5 S

7 D

Figure 4. Functional Block Diagram.

Rev. B 03/14

LYT4221-4228/4321-4328

www.powerint.com

Functional Description

A LYTSwitch device monolithically combines a controller and

high-voltage power FET into one package. The controller

provides both high power factor and constant current output in

a single-stage. The LYTSwitch controller consists of an oscillator,

feedback (sense and logic) circuit, 5.9 V regulator, hysteretic

over-temperature protection, frequency jittering, cycle-by-cycle

current limit, auto-restart, inductance correction, power factor

and constant current control.

FEEDBACK Pin Current Control Characteristics

The ﬁgure shown below illustrates the operating boundaries of

the FEEDBACK pin current. Above IFB(SKIP) switching is disabled

and below IFB(AR) the device enters into auto-restart.

Figure 6. FEEDBACK Pin Current Characteristic.

The FEEDBACK pin current is also used to clamp the maximum

duty cycle to limit the available output power for overload and

open-loop conditions. This duty cycle reduction characteristic

also promotes a monotonic output current start-up characteristic

and helps preventing over-shoot.

REFERENCE Pin

The REFERENCE pin is tied to ground (SOURCE) via an external

resistor. The value selected sets the internal references and it

should be 24.9 kΩ ±1%. One percent resistors are recommended

as the resistor tolerance directly affects the output tolerance.

Other resistor values should not be used.

BYPASS Pin Capacitor Power Gain Selection

LYTSwitch devices have the capability to tailor the internal gain

to either full or a reduced output power setting. This allows

selection of a larger device to minimize dissipation for both

thermal and efﬁciency reasons. The power gain is selected with

the value of the BYPASS pin capacitor. The full power setting is

selected with a 4.7 µF capacitor and the reduced power setting

(for higher efﬁciency) is selected with a 47 µF capacitor. The

BYPASS pin capacitor sets both the internal power gain as well

as the over-current protection (OCP) threshold. Unlike the

larger devices, the LYT4x21 power gain is not programmable.

Use a 47 µF capacitor for the LYT4x21.

Switching Frequency

The switching frequency is 132 kHz during normal operation.

To further reduce the EMI level, the switching frequency is

jittered (frequency modulated) by approximately 5.4 kHz.

During start-up the frequency is 66 kHz to reduce start-up time

when the AC input is phase angle dimmed. Jitter is disabled in

deep dimming.

Soft-Start

The controller includes a soft-start timing feature which inhibits

the auto-restart protection feature for the soft-start period (tSOFT)

to distinguish start-up into a fault (short-circuit) from a large

output capacitor. At start-up the LYTSwitch clamps the

maximum duty cycle to reduce the output power. The total

soft-start period is tSOFT.

Remote ON/OFF and EcoSmart™

The VOLTAGE MONITOR pin has a 1 V threshold comparator

connected at its input. This voltage threshold is used for

remote ON/OFF control. When a signal is received at the

VOLTAGE MONITOR pin to disable the output (VOLTAGE

MONITOR pin tied to ground through an optocoupler photo-

transistor) the LYTSwitch will complete its current switching

cycle before the internal power FET is forced off.

The remote ON/OFF feature can also be used as an eco-mode

or power switch to turn off the LYTSwitch and keep it in a very

low power consumption state for indeﬁnite long periods. When

the LYTSwitch is remotely turned on after entering this mode, it

will initiate a normal start-up sequence with soft-start the next

time the BYPASS pin reaches 5.9 V. In the worst case, the

delay from remote on to start-up can be equal to the full

discharge/charge cycle time of the BYPASS pin. This reduced

consumption remote off mode can eliminate expensive and

unreliable in-line mechanical switches.

IFB(AR)

IFB(DCMAXR)

DC10 DCMAX

IFB(SKIP)

IFB

PI-6978-040213

Skip-Cycle

CC Control

Region

Soft-Start

Region

Auto-Restart

Maximum Duty Cycle

Rev. B 03/14

LYT4221-4228/4321-4328

www.powerint.com

Figure 7. Remote ON/OFF VOLTAGE MONITOR Pin Control.

5.9 V Regulator/Shunt Voltage Clamp

The internal 5.9 V regulator charges the bypass capacitor

connected to the BYPASS pin to 5.9 V by drawing a current

from the voltage on the DRAIN pin whenever the power FET is

off. The BYPASS pin is the internal supply voltage node. When

the power FET is on, the device operates from the energy stored

in the bypass capacitor. Extremely low power consumption of the

internal circuitry allows LYTSwitch to operate continuously from

current it takes from the DRAIN pin. A bypass capacitor value

of 47 or 4.7 µF is sufﬁcient for both high frequency decoupling

and energy storage. In addition, there is a 6.4 V shunt regulator

clamping the BYPASS pin at 6.4 V when current is provided to

the BYPASS pin through an external resistor. This facilitates

powering of LYTSwitch externally through a bias winding to