RT8567GQW - Richtek - Product.Network

RT8567

DS8567-00 April 2011 www.richtek.com

Ordering Information

Note :

Richtek products are :

` RoHS compliant and compatible with the current require-

ments of IPC/JEDEC J-STD-020.

` Suitable for use in SnPb or Pb-free soldering processes.

6-CH 43V WLED Driver

General Description

The RT8567 is a high efficiency driver for white LEDs. It is

designed for LCD panels that employ an array of LEDs a s

the lighting source. An integrated current mode boost

controller drives six strings in parallel a nd supports up to

12 WLEDs per string. The internal current sinks support

a maximum of ±2% current mismatching for excellent

brightness uniformity in each string of LEDs. To provide

enough headroom for current sink operation, the boost

controller monitors the minimum voltage of the feedba ck

pins a nd regulates an optimized output voltage for power

efficiency.

The RT8567 ha s a wide input voltage range from 2.7V to

24V and can provide adjustable LED current from 5mA to

40mA. The internal 250mΩ, 43V power switch with current

mode control provides cycle-by-cycle over current

protection. The RT8567 also integrates PWM dimming

function for a ccurate LED current control. The input PWM

dimming frequency can operate from 200Hz to 25kHz

without inducing any inrush in LED current or inductor

current. The switching frequency of the RT8567 is also

adjustable from 500kHz to 2MHz, which allows flexibility

between efficiency and component size.

The RT8567 is available in a thin WQF N-20L 3x3 package.

Features

z Wide Input Voltage : 2.7V to 24V

z High Output Voltage : Up to 43V

z Channel Current Programmable : 5mA to 40mA

z Channel Current Regulation with Accuracy ±±

±±

±3% and

Matching ±±

±±

±2%

z Dimming Controls : External PWM Input Up to 25kHz

z Adjustable Switching Frequency : 500kHz to 2MHz

z Built-In Soft-Start

z Protections

` LED Strings Open Detection

` Current Limit Protection

` Programmable Over Voltage Protection

` Over Temperature Protection

z 20-Lead WQFN Package

zRoHS Compliant and Halogen Free

Applications

zUMPC and Notebook Computer Backlight

zGPS, Portable DVD Backlight

Pin Configurations

WQFN-20L 3x3

(TOP VIEW)

JY=YM

DNN

Marking Information

JY= : Product Code

YMDNN : Date Code

ISET

VDC

EN PGND

OVP

CH1

CH6

CH5

AGND

PWM

VIN

COMP

17181920

9876

AGND

21 115

NC CH2

CH3

CH4

Package Type

QW : WQFN-20L 3x3 (W-Type)

RT8567

Lead Plating System

G : Green (Halogen Free and Pb Free)

RT8567

www.richtek.com DS8567-00 April 2011

Typical Application Circuit

10µH

OVP

CH1

CH2

CH3

CH6

ISET

PWM

VIN

VOUT

19.6V(MAX)

VIN

3V to 8.5V

6 LEDs by

String

CH5

CH4

10µF

COMP

CIN

L1 D1

9, 21 (Exposed Pad)

AGND

RT8567 ROVP1

ROVP2

COUT

Chip Enable

PWM Signal RT

RRT

51k

10k

10nF 51k

RISET PGND 15

10µF

Open

1VDC

CDC

0.1µF

1µF

OVP setting <24V

10µH

OVP

CH1

CH2

CH3

CH6

ISET

PWM

VIN

VOUT

43V(MAX)

VIN

6V to 24V

12 LEDs by

String

CH5

CH4

10µF

COMP

CIN

L1 D1

9, 21 (Exposed Pad)

AGND

RT8567 ROVP1

ROVP2

COUT

Chip Enable

PWM Signal RT

RRT

51k

10k

10nF 51k

RISET PGND 15

10µF

Open

1VDC

CDC

0.1µF

1µF

Figure 1. Application Circuit 1

Figure 2. Application Circuit 2

RT8567

DS8567-00 April 2011 www.richtek.com

Functional Pin Description

Pi n No. Pi n Name Pin F unc t i on

1 VD C Internal Regulator Voltage. Connect a capacitor to ground.

2 EN Chip Enable Pin (Active High). Note that this pin is high impedance. There

should be a pull low 100kΩ resistor connected to AGND when the control

si gnal is fl oat in g.

3 RT Frequency Set Input. Used to set the switching frequency of the boost

conver ter. Connect a resistor to ground.

4 ISET

LED Current Set Pin. LED Current is Set by the Value of the Resistor RISET

C onnecte d from the I SET Pi n to gr ound. Do n ot short the ISE T pin to gr ound.

VISET i s ty pica l 1V.

5, 13, 17 N C N o In ternal Connecti on.

6 , 7, 8 , CH6 to C H4 Current Si nk Regulation Input. This pin shoul d be connected t o the cathode

of LED s if used. O therwise, i t shoul d be c onnected to gro und.

9, 21 (Exposed Pad) AGND Analog Ground of LE D Driver. The exposed pad m ust be sol der ed t o a large

PC B and connected to AG ND for maximum pow er dis si pat ion.

10,11,12 CH3 to CH1

Current Si nk Regulation Input. This pin shoul d be connected t o the cathode

of LED s if used. O therwise, i t should be c onnected to gro und.

14 O V P O ver Voltage Pro tection fo r B oost Converter. The detecti ng t hre shold is 1.2V.

1 5 PGND Po we r Gr o u nd o f Bo o s t Co nve rt e r .

16 LX S wi t c hing N ode for Boost C onver t er .

18 COMP

Compensation Pin for Error Amplifier. Connect a compensation network to

ground.

1 9 VIN LE D Po wer Supp ly Inp u t.

20 P WM P WM D imm ing C ont r ol Input .

Figure 3. Application Circuit 3

10µH

OVP

CH1

CH2

CH3

CH6

ISET

PWM

VIN

VOUT

19.6V(MAX)

VIN

3V to 8.5V

6 LEDs by

String

CH5

CH4

10µF

COMP

CIN

L1 D1

9, 21 (Exposed Pad)

AGND

RT8567 ROVP1

ROVP2

COUT

PWM Signal RT

RRT

51k

10k

10nF 51k

RISET PGND 15

10µF

Open

1VDC

CDC

0.1µF

1µF

RT8567

www.richtek.com DS8567-00 April 2011

Function Block Diagram

OSC

VDS

OCP &

OTP

Enable

Control

PWM

Controller

Mini LED

Selection

LED Open

Detection

-1.2V

-……

VIN RT OVP

ISET

COMP

CH1

CH2

AGND

CH6

……

PGND

VDC

PWM

RT8567

DS8567-00 April 2011 www.richtek.com

Electrical Characteristics

Recommended Operating Conditions (Note 4)

zSupply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 2.7V to 24V

zJunction T emperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C

zAmbient T emperature Range-------------------------------------------------------------------------------------------- −40°C to 85°C

Absolute Maximum Ratings (Note 1)

zVIN to GND------------------------------------------------------------------------------------------------------------------ −0.3V to 26.5V

zEN, PWM, VDC, ISET, COMP, R T to GND -------------------------------------------------------------------------- −0.3V to 26.5V

zLX to GND ------------------------------------------------------------------------------------------------------------------- −0.3V to 48V

zOVP, (CH1 to CH6) to GND --------------------------------------------------------------------------------------------- −0.3V to 48V

zPower Dissipation, PD @ TA = 25°C

WQFN−20L 3x3------------------------------------------------------------------------------------------------------------ 1.471W

zPa ckage Thermal Resista nce (Note 2)

WQFN−20L 3x3, θJA ------------------------------------------------------------------------------------------------------ 68°C/W

WQFN−20L 3x3, θJC ------------------------------------------------------------------------------------------------------ 7.5°C/W

zLead T emperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°C

zJunction T emperature----------------------------------------------------------------------------------------------------- 150°C

zStorage T emperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C

zESD Susceptibility (Note 3)

HBM -------------------------------------------------------------------------------------------------------------------------- 2kV

MM---------------------------------------------------------------------------------------------------------------------------- 200V

(VIN = 4.5V, TA = 25°C, unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

IVCC V

COMP = 0V, No Switching -- 2 --

VIN Qu ie s c ent C urr e nt IVCC_LX V

COMP = 2V, S wi tc hin g -- 3 --

Shu tdow n Cu rrent ISHDN V

IN = 4. 5V, EN = 0 - - - - 20 μA

VIN Rising -- 2.3 --

V IN U nder Volt age Loc kout

Threshold VUVLO VIN Falling -- 2.1 -- V

C ont r ol Input Logic-High VIH V

IN = 2. 7V to 2 4V 2 - - --

E N I nput Vol tag e

Threshold Logic-Low VIL V

IN = 2. 7V to 2 4V -- -- 0.8

Logic-High VIH V

IN = 2.7V to 24V 1.5 -- --

P WM Input Vol ta ge

Threshold Logic-Low VIL V

IN = 2. 7 V t o 24 V -- -- 0.6 V

Boost Converter RRT = 25kΩ -- 2 --

RRT = 5 1 k Ω 0.9 1 1.1

Sw itching Fr equen cy fOSC RRT = 100kΩ -- 0.5 --

MHz

LX On R esi sta nce (N -MOSF ET) R DS(ON) V

IN > 4. 5 V -- 0 .25 -- Ω

Minimu m On Tim e tMON f

OSC = 1MH z -- 120 -- ns

Maximum Duty DMAX V

COMP = 2 V, Swi tc h i ng -- 9 4 -- %

L X Current Limit ILIM 1.6 2 2.4 A

R egul ated VCHx V

CHx Highest LED St ring, ILED = 20mA -- 0.6 -- V

To be continued

RT8567

www.richtek.com DS8567-00 April 2011

Parameter Symbol Test Conditions Min Typ Max Unit

LED Current P rogr am ming

LE D Cu r ren t Ac cur acy ILEDA 2V > VCHx > 0.6V, RISET = 51kΩ −3 -- 3 %

LE D Cu r ren t M a tc hing ILEDM

2V > VCHx > 0. 6V, RISET = 51kΩ,

Calculating

LEDx AVG

AVG

(I I ) 100%

−× -- ±0.5 ±2 %

ISET Pin Voltage VISET -- 1 -- V

Faul t P r otection

O ver Vol tage T hr eshol d VOVP -- 1.2 -- V

OVP Fault VOVP_FAULT -- 50 -- mV

Ther mal Shutdown

Temperature TSD -- 150 -- °C

LED Channel U nder Voltage

Threshold VLSD No-Connection -- 60 -- mV

Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for

stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the

operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended

periods may remain possibility to affect device reliability.

Note 2. θJA is measured in the natural convection at TA = 25°C on a high effective thermal conductivity four-layer test board of

JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the

package.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions.

RT8567

DS8567-00 April 2011 www.richtek.com

ISET Voltage v s. Temperature

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

-50 -25 0 25 50 75 100 125

Tempera ture (°C)

I SET Voltage (V)

LED Current vs. Te m perature

-50 -25 0 25 50 75 100 125

Temperature (°C)

LED Curr ent (m A)

Typical Operating Characteristics

LED Curre nt vs. Input Voltage

4 8 12 16 20 24

In put V olt age ( V )

Output Current (mA

)

10LEDs per channel, PWM = 3.3V, fOSC = 1MHz

LED1

LED2

LED3

LED4

LED5

LED6

10LEDs per channel, PWM = 3.3V, fOSC = 1MHz

LED Curren t vs. P WM Duty Cycle

0 20406080100

PWM Duty Cycle (%)

LED Current ( m A)

10LEDs per channel, fOSC = 1MHz

PWM = 200Hz

PWM = 1kHz

PWM = 10kHZ

PWM = 25kHz

10LEDs per channel, fOSC = 1MHz

Efficiency vs. Input Voltage

100

4 8 12 16 20 24

In put Voltage (V)

Eff iciency (%)

60LEDs, PWM = 3.3V, fOSC = 1MHz

ISET Voltage vs. Input Voltage

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

4 8 12 16 20 24

In put Vol ta ge (V)

I SET Volt age ( V)

10LEDs per channel, fOSC = 1MHz

RT8567

www.richtek.com DS8567-00 April 2011

OVP Threshold Voltage vs. Input Voltage

1.0

1.1

1.2

1.3

1.4

1.5

4 8 12 16 20 24

In put Voltage (V)

OVP Threshold V oltage (V)

10LEDs per channel, fOSC = 1MHz

Line Transient Response

Time (50ms/Div)

VIN = 11V to 14V, PWM = 3.3V, f OSC = 1MHz

VIN

(5V/Div)

ILED

(50mA/Div)

Power On from EN

Time (5ms/Div)

VEN

(5V/Div)

VOUT

(20V/Div)

ILED

(20mA/Div)

VIN = 12V, PWM = 3.3V, fOSC = 1MHz

Power Off from EN

Time (25ms/Div)

VEN

(5V/Div)

VOUT

(20V/Div)

ILED

(20mA/Div)

VIN = 12V, PWM = 3.3V, fOSC = 1MHz

Quiescent Current vs. Temperature

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

-50 -25 0 25 50 75 100 125

Temperatur e (°C)

Quiescent C urrent ( m A) 1

VIN = 12V, f OSC = 1MHz

Line Transient Response

Time (50ms/Div)

VIN

(2V/Div)

ILED

(50mA/Div) VIN = 4.5V to 5.5V, PWM = 3.3V, fOSC = 1MHz

RT8567

DS8567-00 April 2011 www.richtek.com

Application Information

The RT8567 is a current mode boost converter ca pable of

powering to 72 white LEDs with a progra mma ble current

for uniform intensity . The part integrates current sources,

soft-start, and easy analog and digital dimming control.

The protection block provides the circuitry for over

temperature, over voltage and current limit protection

features.

Input UVLO

The input operating voltage ra nge of the RT8567 is from

2.7V to 24V. An input ca pa citor at the VIN pin ca n reduce

ripple voltage. It is re commended to use a cera mic 10μF

or larger capacitance as the input capacitor. This IC provides

an Under Voltage Lockout (UVLO) function to enhance

the stability during startup. The UVLO threshold of the

input rising voltage is set at 2.3V typically with a 0.2V

hysteresis.

Soft-Start

The function of the soft-start is defined by two periods.

The first period is capped at the peak current limit with

the time decided by the ratio of VOUT and VIN. However ,

an external capacitor, VOUT, can also affect the time of

charging. The second period is defined by the slowly

ra mping of the ILED current by the ISET voltage. Thus, the

inrush current is limited by the boost converter and current

regulator.

Compensation

The control loop can be compensated by adjusting the

external components connected to the COMP pin. The

COMP pin is the output of the internal error a mplifier . The

compensation capacitors, C3 and C4, will adjust the

integrator zero and pole respectively to maintain stability .

Moreover, the resistor, R3, will adjust the frequency

integrator gain for fa st tra nsient response.

LED Connection

The RT8567 equips 6-CH LED drivers with each channel

supporting up to 12 LEDs. The 6 LED strings are

connected from VOUT to pin 6, 7, 8, 10, 11, and 12

respectively. If one of the LED channels is not used, the

unused LED pin should be opened directly.

Setting and Regulation of LED current

The LED current can be calculated by the following

equation :

LED ISET

1020

I = R

where, RISET is the resistor between the ISET pin and

GND.

This setting is the reference for the LED current at CH1 to

CH6 and represents the sensed LED current for each string.

The DC/DC converter regulates the LED current according

to the setting.

Brightness Control

The RT8567 brightness dimming is determined by the

signal on the PWM pin with a suggested PWM frequency

range from 200Hz to 25kHz. Referring to the following curve,

the minimum dimming duty can be as low as 1% for the

frequency ra nge from 200Hz to 1kHz. For the frequency

range from 1kHz to 10kHz, the dimming duty is at most

5%. If the frequency is increased to 25kHz, the dimming

duty will be up to 10%.

Over Voltage Protection

The RT8567 equips an Over Voltage Protection (OVP)

function. When the voltage at the OVP pin reaches a

threshold of a pproximately 1.2V , the MOSFET driver turns

off. The MOSFET driver turns on again once the voltage

at OVP drops below the threshold voltage. Thus, the

LED Curren t vs. P WM Duty Cycle

0 20406080100

PWM Duty Cycle (%)

LED Current ( m A)

PWM = 200Hz

PWM = 1kHz

PWM = 10kHZ

PWM = 25kHz

Figure 1

RT8567

www.richtek.com DS8567-00 April 2011

)×OVP2

OUT, OVP OVP OVP1

1+R

V = V(

where ROVP1 and ROVP2 are the resistors in the voltage

divider connected to the OVP pin. If at least one string is

in normal operation, the controller will automatically ignore

the open strings a nd continue to regulate the current f or

the string(s) in normal operation.

Current Limit Protection

The RT8567 can limit the peak current to achieve over

current protection. The RT8567 senses the inductor

current through LX pin in the ON period. The duty cycle

depends on the current sense signal summed with the

internal slope compensation a nd compared to the COMP

signal. The internal N-MOSFET will be turned off when

the current signal is larger than the COMP signal. In the

OFF period, the inductor current will descend. The internal

MOSFET is turned on by the oscillator in the next starting

cycle.

Over Temperature Protection

The RT8567 has an over temperature protection (OTP)

function to prevent excessive power dissipation from

overheating the device. The OTP will shut down switching

operation when the junction temperature exceeds 150°C.

Inductor Selection

The value of the output inductor (L), where the tra nsition

from discontinuous to continuous mode occurs is

a pproxi mated by the following equation :

output voltage ca n be cla mped at a certain voltage level.

This voltage level can be calculated by the following

equation :

−×

×××

OUT IN IN2

OUT OUT

(V V ) V

L = 2I fV

where,

VOUT = maximum output voltage.

VIN = minimum input voltage.

f = operating frequency .

IOUT = sum of current from all LED strings.

η is the eff iciency of the power converter .

The boost converter operates in discontinuous mode over

())

×−

=×

OUT OUT OUT IN

PEAK IN OUT

VI VV

I) + ((

x V 2 L V

Diode Selection

Schottky diode is a good choice for any asynchronous

boost converter due to its small forward voltage a nd fast

switching Speed. However, when selecting a Schottky

diode, important parameters such as power dissipation,

reverse voltage rating and pulsating peak current must all

be taken into consideration. Choose a suitable diode with

reverse voltage rating greater tha n the maxi mum output

voltage.

Capacitor Selection

The input ca pacitor reduces current spikes from the input

supply and minimizes noise injection to the converter. For

most a pplications, a 10μF cera mic ca p acitor is suf ficient.

A value higher or lower may be used depending on the

noise level from the input supply a nd the input current to

the converter. It is recommended to choose a ceramic

ca pacitor based on the output voltage ripple requirements.

The minimum value of the output capacitor COUT, can be

calulated by the following equation :

the entire input voltage ra nge when the L1 inductor value

is less tha n this value L. With a n inductance gre ater than

L, the converter operates in continuous mode at the

minimum input voltage and may be discontinuous at higher

voltages.

The selected inductor must be selected with saturation

current rating greater than the peak current provided by

the following equation :

−×

×××

OUT IN OUT

OUT RIPPLE OUT

(V V ) I

C = VVf

Thermal Considerations

For continuous operation, do not exceed absolute

maximum junction temperature. The maximum power

dissipation depends on the thermal resistance of the IC

package, PCB layout, rate of surrounding airflow, and

difference between junction and ambient temperature. The

maximum power dissipation can be calculated by the

following formula :

PD(MAX) = (TJ(MAX) − TA) / θJA

RT8567

DS8567-00 April 2011 www.richtek.com

Figure 2. Derating Curve for RT8567 Package

where TJ(MAX) is the maximum junction temperature, TA is

the a mbient temperature, and θJA is the junction to ambient

thermal resistance.

For recommended operating condition specifications of

the RT8567, the maximum junction temperature is 125°C

and TA is the ambient temperature. The junction to a mbient

thermal resistance, θJA, is layout dependent. For

WQFN-20L 3x3 pa ckages, the thermal resistance, θJA, is

68°C/W on a standard JEDEC 51-7 four-layer thermal test

board. The maximum power dissipation at TA = 25°C can

be calculated by the following formula :

PD(MAX) = (125°C − 25°C) / (68°C/W) = 1.471W for

WQF N-20L 3x3 package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

resistance, θJA. For the RT8567 package, the derating

curve in Figure 2 allows the designer to see the effect of

rising ambient temperature on the maximum power

dissipation.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 25 50 75 100 125

Ambien t Tempera tu re (°C)

Maximum Power Dissipati on (W ) 1

Four-Layer PCB

Layout Considerations

PCB layout is very important for designing switching power

converter circuits. The following layout guides should be

strictly followed for best performa nce of the RT8567.

`The power components L1, D1, CIN, COUT must be placed

as close to the IC as possible to reduce current loop.

The PCB trace between power components must be as

short a nd wide as possible.

`Place L1 and D1 as close to the LX pin a s possible. The

tra ce should be as short a nd wide as possible.

`The compensation circuit should be kept away from

the power loops and shielded with a ground trace to

prevent any noise coupling. Place the compensation

components as close to the COMP pin as possible.

`The exposed pad of the chip should be connected to

ground plane for thermal consideration.

Figure 3. PCB Layout Guide

GND

ISET

VDC

EN PGND

OVP

CH1

CH6

CH5

AGND

PWM

VIN

COMP

17181920

9876

AGND

21 115

NC CH2

CH3

CH4

GND

RISET

VOUT

VIN

CIN

Place the power

components as

Close as possible.

The traces should

be wide and short

especially for the

high current loop.

The compensation circ uit s hould be k ept away from The power loops

and shielded with a ground trace to prevent any noise coupling.

Locate the C2 as

close to VIN as

possible.

Locate RISET as

close to ISET

as possible.

COUT

RT8567

www.richtek.com DS8567-00 April 2011

Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit

design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be

guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.

Richtek Technology Corporation

Headquarter

5F, No. 20, Taiyuen Street, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789 Fax: (8863)5526611

Richtek Technology Corporation

Taipei Office (Marketing)

5F, No. 95, Minchiuan Road, Hsintien City

Taipei County, Taiwan, R.O.C.

Tel: (8862)86672399 Fax: (8862)86672377

Email: marketing@richtek.com

Outline Dimension

Dimension s In Millimeters Dimen sio ns In Inches

Symbol Min Max Min Max

A 0.700 0.800 0.028 0.031

A1 0.000 0.050 0.000 0.002

A3 0.175 0.250 0.007 0.010

b 0.150 0.250 0.006 0.010

D 2.900 3.100 0.114 0.122

D2 1.650 1.750 0.065 0.069

E 2.900 3.100 0.114 0.122

E2 1.650 1.750 0.065 0.069

e 0.400 0.016

L 0.350 0.450

0.014 0.018

W-Type 20L QFN 3x3 Package

Note : The configuration of the Pin #1 identifier is optional,

but must be located within the zone indicated.

DETAIL A

Pin #1 ID a nd T ie Bar M ark Options