RT8020GQW - Richtek Technology

RT8020

DS8020-06 March 2012 www.richtek.com

Applications

Mobile Phones

Personal Information Appliances

Wireless and DSL Modems

MP3 Players

Portable Instruments

Ordering Information

Pin Configurations

(TOP VIEW)

WDFN-12L 3x3

Dual High-Efficiency PWM Step-Down DC/DC Converter

Features



2.5V to 5.5V Input Range



Adjustable Output From 0.6V to VIN



1.2V, 1.3V, 1.8V, 2.5V and 3.3V Fixed/ Adjustable

Output Voltage



1A Output Current



95% Efficiency



No Schottky Diode Required



50uA Quiescent Current per Channel



1.5MHz Fixed Frequency PWM Operation



Small 12-Lead WDFN Package



RoHS Compliant and 100% Lead (Pb)-Free

General Description

The RT8020 is a dual high-efficiency Pulse-Width-

Modulated (PWM) step-down DC/DC converter. It is

capable of delivering 1A output current over a wide input

voltage range from 2.5V to 5.5V, the RT8020 is ideally

suited for portable electronic devices that are powered

from 1-cell Li-ion battery or from other power sources within

the range such as cellular phones, PDAs and other hand-

held devices.

Two operational modes are available : PWM/Low-Dropout

auto-switch and shutdown modes. Internal synchronous

rectifier with low RDS(ON) dramatically reduces conduction

loss at PWM mode. No external Schottky diode is

required in practical application.

The RT8020 enters Low-Dropout mode when normal PWM

cannot provide regulated output voltage by continuously

turning on the upper PMOS. The RT8020 enter shutdown

mode and consumes less than 0.1μA when EN pin is pulled

low.

The switching ripple is easily smoothed-out by small

package filtering elements due to a fixed operation

frequency of 1.5MHz. This along with small

WDFN-12L 3x3 package provides small PCB area

application. Other features include soft start, lower internal

reference voltage with 2% accuracy, over temperature

protection, and over current protection.

VIN2

LX2

NC1

FB1

EN2

NC2

FB2

LX1

GND

EN1 VIN1

GND

RT8020

Package Type

QW : WDFN-12L 3x3 (W-Type)

Lead Plating System

P : Pb Free

G : Green (Halogen Free and Pb Free)

Output Voltage : VOUT1/VOUT2

Default : Adjustable

A : 3.3V/1.8V

B : 3.3V/1.3V

C : 3.3V/1.2V

D : 2.5V/1.8V

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.

RT8020

DS8020-06 March 2012www.richtek.com

Typical Application Circuit

Figure 1. Adjustable Voltage Regulator

(

)

Rx2

Rx1

1 VV REFOUTx +×=

EN2

NC2

FB2

VIN2

LX2

FB1

RT8020

GND

LX1

GND

5NC1

3, Exposed Pad (13)

VOUT2

2.2µH

850k

4.7µF

CIN2

22pF

VIN1 7

6EN1 VIN1

4.7µF

2.2µH

R22

4.7µF

VOUT1

850k

22pF

4.7µF

R12

VIN2

C11

COUT1

CIN1

COUT2

C21

R11

R21

Marking Information

RT8020APQW

C2-YM

DNN

RT8020AGQW

C2- : Product Code

YMDNN : Date Code

RT8020BPQW

C3= : Product Code

YMDNN : Date Code

C3=YM

DNN

RT8020BGQW

C3-YM

DNN

C3- : Product Code

YMDNN : Date Code

C4=YM

DNN

C4-YM

DNN

C5=YM

DNN

C5-YM

DNN

RT8020CPQW

C2=YM

DNN

C2= : Product Code

YMDNN : Date Code

C4- : Product Code

YMDNN : Date Code

RT8020CGQW

C4= : Product Code

YMDNN : Date Code

RT8020DPQW

C5- : Product Code

YMDNN : Date Code

RT8020DGQW

C5=: Product Code

YMDNN : Date Code

RT8020

DS8020-06 March 2012 www.richtek.com

Figure 2. Fixed Voltage Regulator

VOUTx = 1.2V, 1.3V, 1.8V, 2.5V or 3.3V

Functional Pin Description

Pin No. Pin Name Pin Function

1 VIN2 Power Input of Channel 2.

2 LX2 Pin for Switching of Channel 2.

3, 9,

Exposed Pad (13) GND Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

4 FB1 Feedback of Channel 1.

5, 11 NC1, NC2 No Connection or Connect to VIN.

6 EN1 Chip Enable of Channel 1 (Active High). VEN1 ≦ VIN1.

7 VIN1 Power Input of Channel 1.

8 LX1 Pin for Switching of Channel 1.

10 FB2 Feedback of Channel 2.

12 EN2 Chip Enable of Channel 2 (Active High). VEN2 ≦ VIN2.

EN2

NC2

FB2

VIN2

LX2

FB1

RT8020

GND

LX1

GND

5NC1

VOUT2

2.2µH

CIN2

4.7µF

VIN1 7

6EN1 VIN1

4.7µF

2.2µH

4.7µF

VOUT1

4.7µF

VIN2

COUT1

CIN1

COUT2

3, Exposed Pad (13)

RT8020

DS8020-06 March 2012www.richtek.com

Function Block Diagram

Driver

Control

Logic

Current Limit

Detector

OSC and

Shutdown

Control

Current

Sense

VREF

FBx

GND

LXx

PWM

Comparator

Slope

Compensation

Error

Amplifier

UVLO and

Power Good

Detector

COMP

ENx VINx

RS1

RS2

RT8020

DS8020-06 March 2012 www.richtek.com

Absolute Maximum Ratings (Note 1)

Supply Input Voltage, VIN1, VIN2 ---------------------------------------------------------------------------------- −0.3V to 6.5V

EN1, FB1, LX1, EN2, FB2 and LX2 Pin Voltage -------------------------------------------------------------- −0.3V to (VIN + 0.3V)

Power Dissipation, PD @ TA = 25°C

WDFN-12L 3x3 -------------------------------------------------------------------------------------------------------- 1.667W

Package Thermal Resistance (Note 2)

WDFN-12L 3x3, θJA -------------------------------------------------------------------------------------------------- 60°C/W

WDFN-12L 3x3, θJC -------------------------------------------------------------------------------------------------- 8.2°C/W

Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------- 260°C

Junction Temperature ------------------------------------------------------------------------------------------------ 150°C

Storage Temperature Range --------------------------------------------------------------------------------------- −65°C to 150°C

ESD Susceptibility (Note 3)

HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV

MM (Machine Mode) ------------------------------------------------------------------------------------------------- 200V

Electrical Characteristics

Parameter Symbol Test Conditions Min Typ Max Unit

Channel 1 an d Channel 2

Input Voltage Range VIN 2.5 -- 5.5 V

Under Voltage Lock Out

threshold UVLO -- 1.8 -- V

Hysteresis -- 0.1 -- V

Quiescent Current IQ I

OU T = 0mA, VFB = VREF + 5% -- 50 70 μA

Shutdown Current ISHDN EN = GND -- 0.1 1 μA

Reference Voltage VREF For Adjustable Output Voltage 0.588 0.6 0.612 V

Adjustable Output Voltage

Range VOUT (Note 6) VREF -- VIN −ΔV V

ΔVOUT VIN = 2.5V to 5.5V, VOUT = 1.2V

0A < IOUT < 1A −3 -- 3 %

ΔVOUT VIN = 2.5V to 5.5V, VOUT = 1.3V

0A < IOUT < 1A −3 -- 3 %

ΔVOUT VIN = 2.5 to 5.5V, VOUT = 1.8V

0A < IOUT < 1A −3 -- 3 %

ΔVOUT VIN = VOUT + ΔV to 5.5V (Note 5)

VOUT = 2.5V, 0A < IOU T < 1A −3 -- 3 %

Output Voltage

Accuracy Fix

ΔVOUT VIN = VOUT + ΔV to 5.5V (Note 5)

VOUT = 3.3V, 0A < IOU T < 1A −3 -- 3 %

Recommended Operating Conditions (Note 4)

Supply Input Voltage ------------------------------------------------------------------------------------------------- 2.5V to 5.5V

Junction Temperature Range --------------------------------------------------------------------------------------- −40°C to 125°C

Ambient Temperature Range --------------------------------------------------------------------------------------- −40°C to 85°C

(VIN = 3.6V, VOUT = 2.5V, VREF = 0.6V, L = 2.2uH, CIN = 4.7μF, C OUT = 10μF, TA = 25° C, IMAX= 1A unless otherwise specified)

RT8020

DS8020-06 March 2012www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Unit

Output Voltage

Accuracy Adjustable ΔVOUT VIN = VOUT + ΔV to 5.5V (Note 5)

0A < IOUT < 1A −3 -- 3 %

FB Input Current IFB V

FB = VIN −50 -- 50 nA

VIN = 2.5V -- 0.38 --

RDS(ON) of P-MOSFET RDS(ON)_P IOUT = 200mA VIN = 3.6V -- 0.28 -- Ω

VIN = 2.5V -- 0.35 --

RDS(ON) of N-MOSFET RDS(ON)_N IOUT = 200mA VIN = 3.6V -- 0.25 -- Ω

P-Channel Current Limit ILIM_P VIN = 2.5V to 5.5 V 1.4 1.5 -- A

Logic-High VEN_H V

IN = 2.5V to 5.5V 1.5 -- VIN

EN Input Voltage

Logic-Low VEN_L V

IN = 2.5V to 5.5V -- -- 0.4

Oscillator Frequency fOSC V

IN = 3.6V, IOUT = 100mA 1.2 1.5 1.8 MHz

Thermal Shutdown Temperature TSD -- 160 -- °C

Maximum Duty Cycle 100 -- -- %

LX Leakage Current ILX V

IN = 3.6V, VLX = 0V or VLX = 3.6V −1 -- 1 μA

Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are

stress ratings only, and 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 may

affect device reliability.

Note 2. θ

JA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is

measured at the exposed pad of the package.

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

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

Note 5. ΔV = IOUT x PRDS(ON)

Note 6. Guarantee by design.

RT8020

DS8020-06 March 2012 www.richtek.com

Typical Operating Characteristics

Efficiency vs. Output Current

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Output Current (A)

Efficiency (%)

VIN = 3.6V

VIN = 4.2V

VIN = 5.0V

VOUT = 3.3V, L = 4.7μH, COUT = 4.7μF

Efficiency vs. Output Current

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Output Current (A)

Efficiency (%)

VIN = 5.0V

VIN = 3.6V

VIN = 3.3V

VIN = 2.5V

VOUT = 1.2V, L = 4.7μH, COUT = 4.7μF

Efficiency vs. Output Current

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Output Current (A)

Efficiency (%)

VIN = 5.0V

VIN = 3.6V

VIN = 3.3V

VIN = 2.5V

VOUT = 1.2V, L = 2.2μH, COUT = 10μF

EN Pin Threshold vs . Tem pe rature

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

-40 -25 -10 5 20 35 50 65 80 95 110 125

Temperature

EN Pin Threshold (V)

VIN = 3.6V, VOUT = 1.2V, IOUT = 0A

Rising

Falling

(°C)

UVLO Threshold vs. Temperature

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

-40 -25 -10 5 20 35 50 65 80 95 110 125

Temperature

UVLO Threshold (V)

(°C)

VOUT = 1.2V, IOUT = 0A

Rising

Falling

EN Pin Threshol d vs. Input Voltage

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5

Input Voltage (V)

EN Pin Threshold (V)

VOUT = 1.2V, IOUT = 0A

Rising

Falling

EN Pin Threshold vs. Input Voltage

RT8020

DS8020-06 March 2012www.richtek.com

Output Current Limit vs. Te m pe rature

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

-40 -25 -10 5 20 35 50 65 80 95 110 125

Temperature

Output Current Limit (A)

(°C)

VOUT = 1.2V

VIN = 5.0V

VIN = 3.6V

VIN = 3.3V

Switching Frequency vs. Temperature

1.2

1.25

1.3

1.35

1.4

1.45

1.5

1.55

1.6

-40 -25 -10 5 20 35 50 65 80 95 110 125

Temperature

Frequency(kHz)

VIN = 3.6V, VOUT = 1.2V, IOUT = 300mA

(°C)

Output Voltage vs. Loading Current

1.180

1.185

1.190

1.195

1.200

1.205

1.210

1.215

1.220

1.225

1.230

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Loading Current (A)

Output Voltage (V)

VIN = 5.0V

VIN = 3.6V

Output Voltage vs. Te m perature

1.15

1.16

1.17

1.18

1.19

1.20

1.21

1.22

1.23

1.24

1.25

-40 -25 -10 5 20 35 50 65 80 95 110 125

Temperature

Output Voltage (V)

VIN = 3.6V, IOUT = 0A

(°C)

Switching Frequency vs. Input Voltage

1.20

1.25

1.30

1.35

1.40

1.45

1.50

1.55

1.60

2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5

Input Voltage (V)

Frequency(kHz)

VIN = 3.6V, VOUT = 1.2V, IOUT = 300mA

Output Current Limit vs . Input Voltage

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5

Input Voltage (V)

Output Current Limit (A)

VOUT = 1.2V @ TA = 25°C

RT8020

DS8020-06 March 2012 www.richtek.com

Power On from VIN

VIN

(2V/Div)

Time (250μs/Div)

VOUT

(1V/Div)

ILX

(1A/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA

Load Transient Response

Time (50μs/Div)

VOUT

(50mV/Div)

IOUT

(500mA/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 0.5A

Power On from EN

VEN

(2V/Div)

Time (100μs/Div)

VOUT

(1V/Div)

IIN

(500mA/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA

Power On from EN

VEN

(2V/Div)

Time (100μs/Div)

VOUT

(1V/Div)

IIN

(500mA/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 1A

Load Transient Response

Time (50μs/Div)

VOUT

(50mV/Div)

IOUT

(500mA/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 1A

Power Off from EN

VEN

(2V/Div)

Time (100μs/Div)

VOUT

(1V/Div)

ILX

(1A/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA

RT8020

DS8020-06 March 2012www.richtek.com

Ripple

Time (500ns/Div)

VOUT

(10mV/Div)

VLX

(2V/Div)

VIN = 3.6V, VOUT = 1.2V, IOUT = 1A

Ripple

Time (500ns/Div)

VOUT

(10mV/Div)

VLX

(2V/Div)

VIN = 5.0V, VOUT = 1.2V, IOUT = 1A

Load Transient Response

Time (50μs/Div)

VOUT

(50mV/Div)

IOUT

(500mA/Div)

VIN = 5.0V, VOUT = 1.2V, IOUT = 50mA to 1A

Load Transient Response

Time (50μs/Div)

VOUT

(50mV/Div)

IOUT

(500mA/Div)

VIN = 5.0V, VOUT = 1.2V, IOUT = 50mA to 0.5A

RT8020

DS8020-06 March 2012 www.richtek.com

Applications Information

The basic RT8020 application circuit is shown in Typical

Application Circuit. External component selection is

determined by the maximum load current and begins with

the selection of the inductor value and operating frequency

followed by CIN and COUT.

Inductor Selection

For a given input and output voltage, the inductor value

and operating frequency determine the ripple current. The

ripple current ΔIL increases with higher VIN and decreases

with higher inductance.

Having a lower ripple current reduces the ESR losses in

the output capacitors and the output voltage ripple. Highest

efficiency operation is achieved at low frequency with small

ripple current. This, however, requires a large inductor.

A reasonable starting point for selecting the ripple current

is ΔIL = 0.4(IMAX). The largest ripple current occurs at the

highest VIN. To guarantee that the ripple current stays

below a specified maximum, the inductor value should be

chosen according to the following equation :

Inductor Core Selection

Once the value for L is known, the type of inductor must

be selected. High efficiency converters generally cannot

afford the core loss found in low cost powdered iron cores,

forcing the use of more expensive ferrite or permalloy

cores. Actual core loss is independent of core size for a

fixed inductor value but it is very dependent on the

inductance selected. As the inductance increases, core

losses decrease. However, increased inductance requires

more turns of wire and therefore copper losses will

increase.

Ferrite designs have very low core losses and are preferred

at high switching frequencies, so design goals can

concentrate on copper loss and preventing saturation.

Ferrite core material saturates “hard”, which means that

inductance collapses abruptly when the peak design

current is exceeded.

This formula has a maximum at VIN = 2VOUT, where

IRMS = IOUT/2. This simple worst-case condition is

commonly used for design because even significant

deviations do not offer much relief. Note that ripple current

ratings from capacitor manufacturers are often based on

only 2000 hours of life which makes it advisable to further

de-rate the capacitor, or choose a capacitor rated at a

higher temperature than required. Several capacitors may

also be paralleled to meet size or height requirements in

the design.

The selection of COUT is determined by the effective series

resistance (ESR) that is required to minimize voltage ripple

and load step transients, as well as the amount of bulk

capacitance that is necessary to ensure that the control

loop is stable. Loop stability can be checked by viewing

the load transient response as described in a later section.

The output ripple, ΔVOUT, is determined by :

⎥

⎦

⎤

⎢

⎣

⎡−×

⎥

⎦

⎤

⎢

⎣

⎡

OUTOUT

ΔI

⎥

⎦

⎤

⎢

⎣

⎡−×

⎥

⎦

⎤

⎢

⎣

⎡

Δ×

IN(MAX)

OUT

L(MAX)

OUT

⎥

⎦

⎤

⎢

⎣

⎡+≤

OUT

LOUT 8fC

ESR ΔIΔV

OUT

OUT(MAX)RMS −=

This results in an abrupt increase in inductor ripple current

and consequent output voltage ripple.

Do not allow the core to saturate!

Different core materials and shapes will change the size/

current and price/current relationship of an inductor. Toroid

or shielded pot cores in ferrite or permalloy materials are

small and don't radiate energy but generally cost more

than powdered iron core inductors with similar

characteristics. The choice of which style inductor to use

mainly depend on the price vs. size requirements and

any radiated field/EMI requirements.

CIN and COUT Selection

The input capacitance, CIN, is needed to filter the

trapezoidal current at the source of the top MOSFET. To

prevent large ripple voltage, a low ESR input capacitor

sized for the maximum RMS current should be used. RMS

current is given by :

RT8020

DS8020-06 March 2012www.richtek.com

The output ripple is highest at maximum input voltage

since ΔIL increases with input voltage. Multiple capacitors

placed in parallel may be needed to meet the ESR and

RMS current handling requirements. Dry tantalum, special

polymer, aluminum electrolytic and ceramic capacitors are

all available in surface mount packages. Special polymer

capacitors offer very low ESR but have lower capacitance

density than other types. Tantalum capacitors have the

highest capacitance density but it is important to only

use types that have been surge tested for use in switching

power supplies. Aluminum electrolytic capacitors have

significantly higher ESR but can be used in cost-sensitive

applications provided that consideration is given to ripple

current ratings and long-term reliability. Ceramic capacitors

have excellent low ESR characteristics but can have a

high voltage coefficient and audible piezoelectric effects.

The high Q of ceramic capacitors with trace inductance

can also lead to significant ringing.

Using Ceramic In put and Output Capacitors

Higher values, lower cost ceramic capacitors are now

becoming available in smaller case sizes. Their high ripple

current, high voltage rating and low ESR make them ideal

for switching regulator applications. However, care must

be taken when these capacitors are used at the input and

output. When a ceramic capacitor is used at the input

and the power is supplied by a wall adapter through long

wires, a load step at the output can induce ringing at the

input, VIN. At best, this ringing can couple to the output

and be mistaken as loop instability. At worst, a sudden

inrush of current through the long wires can potentially

cause a voltage spike at VIN large enough to damage the

part.

Output Voltage Programming

The resistive divider allows the FB pin to sense a fraction

of the output voltage as shown in Figure 3.

Figure 3. Setting the Output Voltage

For adjustable voltage mode, the output voltage is set by

an external resistive divider according to the following

equation :

VOUT = VREF x (1+ R1/R2)

Where VREF is the internal reference voltage (0.6V typical)

Efficiency Considerations

The efficiency of a switching regulator is equal to the output

power divided by the input power times 100%. It is often

useful to analyze individual losses to determine what is

limiting the efficiency and which change would produce

the most improvement. Efficiency can be expressed as :

Efficiency = 100% − (L1+ L2+ L3+...)

where L1, L2, etc. are the individual losses as a percentage

of input power. Although all dissipative elements in the

circuit produce losses, two main sources usually account

for most of the losses: VIN quiescent current and I2R

losses.

The VIN quiescent current loss dominates the efficiency

loss at very low load currents whereas the I2R loss

dominates the efficiency loss at medium to high load

currents. In a typical efficiency plot, the efficiency curve

at very low load currents can be misleading since the

actual power lost is of no consequence.

1.The VIN quiescent current oppears due to two

components : the DC bias current and the gate charge

currents. The gate charge current results from switching

the gate capacitance of the internal power MOSFET

switches. Each time the gate is switched from high to

low to high again, a packet of charge ΔQ moves from VIN

to ground.

The resulting ΔQ/Δt is the current out of VIN that is typically

larger than the DC bias current. In continuous mode,

IGATECHG = f(QT + QB)

where QT and QB are the gate charges of the internal top

and bottom switches. Both the DC bias and gate charge

losses are proportional to VIN and thus their effects will

be more pronounced at higher supply voltages.

2. I2R losses are calculated from the resistances of the

internal switches, RSW and external inductor RL. In

continuous mode the average output current flowing

RT8020

GND

VOUT

RT8020

DS8020-06 March 2012 www.richtek.com

Checking Tran sient Re spon se

The regulator loop response can be checked by looking

at the load transient response. Switching regulators take

several cycles to respond to a step in load current. When

a load step occurs, VOUT immediately shifts by an amount

equal to ΔILOAD (ESR), where ESR is the effective series

resistance of COUT. ΔILOAD also begins to charge or

discharge COUT generating a feedback error signal used

by the regulator to return VOUT to its steady-state value.

During this recovery time, VOUT can be monitored for

overshoot or ringing that would indicate a stability problem.

Layout Considerations

Follow the PCB layout guidelines for optimal performance

of RT8020.

`For the main current paths, keep their traces short and

wide.

`Put the input capacitor as close as possible to the device

pins (VIN and GND).

`LX node is with high frequency voltage swing and should

be kept small area. Keep analog components away from

LX node to prevent stray capacitive noise pick-up.

`Connect feedback network behind the output capacitors.

Keep the loop area small. Place the feedback

components near the RT8020.

`Connect all analog grounds to a command node and

then connect the command node to the power ground

behind the output capacitors.

through inductor L is “chopped” between the main switch

and the synchronous switch. Thus, the series resistance

looking into the LX pin is a function of both top and bottom

MOSFET RDS(ON) and the duty cycle (DC) is shown as

follows :

RSW = RDS(ON)TOP x DC + RDS(ON)BOT x (1 − DC)

The RDS(ON) for both the top and bottom MOSFETs can be

obtained from the Typical Performance Characteristics

curves. Thus, to obtain I2R losses, simply add RSW to RL

and multiply the result by the square of the average output

current. Other losses including CIN and COUT ESR

dissipative losses and inductor core losses generally

account for less than 2% of the total loss.

Thermal Considerations

The maximum power dissipation depends on the thermal

resistance of IC package, PCB layout, the rate of

surroundings airflow and temperature difference between

junction to ambient. The maximum power dissipation can

be calculated by following formula :

PD(MAX) = ( TJ(MAX) − TA ) / θJA

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

the ambient temperature and the θJA is the junction to

ambient thermal resistance. For recommended operating

conditions specification of RT8020 DC/DC converter,

where TJ(MAX) is the maximum junction temperature of

the die and TA is the ambient temperature. The junction

to ambient thermal resistance θJA is layout dependent.

For WDFN-12L 3x3 packages, the thermal resistance

θJA is 60°C/W on the standard JEDEC 51-7 four-layers

thermal test board. The maximum power dissipation at

TA = 25°C can be calculated by following formula :

PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W for

WDFN-12L 3x3 packages

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance θJA. For RT8020 packages, the Figure 4 of de-

rating curves allows the designer to see the effect of rising

ambient temperature on the maximum power allowed.

Figure 4. De-rating Curves for RT8020 Package

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 25 50 75 100 125

Ambient Temperature (°C)

Maximum Power Dissipation (W)

Four-Layer PCB

RT8020

14 DS8020-06 March 2012www.richtek.com

Table 1. Recommended Induct or s

Component

Supplier Ser ies Inductance

(μH) DCR

(mΩ) C urren t Ra ti ng

(mA) Di mensions

(mm)

TAI YO YUDEN NR 3015 2.2 60 1480 3 x 3 x 1.5

TAI YO YUDEN NR 3015 4.7 120 1020 3 x 3 x 1.5

Sumida CDRH2D14 2.2 75 1500 4.5 x 3.2 x 1.55

Sumida CDRH2D14 4.7 135 1000 4.5 x 3.2 x 1.55

GOTREND GTSD 32 2. 2 58 1500 3. 85 x 3.85 x 1. 8

GOTREND GTSD 32 4. 7 146 1100 3. 85 x 3 .85 x 1. 8

Table 2. R ecommended Capacitors for CIN and C OUT

Co m pon ent Sup pl ier Pa rt No. C apaci tance (μF) Case Size

TDK C1608JB0J475M 4.7 0603

TDK C2012JB0J106M 10 0805

MURATA GRM188R60J475KE19 4.7 0603

MURATA GRM219R60J106ME19 10 0805

TAIYO YUDEN JMK107BJ475RA 4.7 0603

TAIYO YUDEN JMK107BJ106MA 10 0603

TAIYO YUDEN JMK212BJ106RD 10 0805

RT8020

DS8020-06 March 2012 www.richtek.com

Richtek Technology Corporation

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

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789

Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should

obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot

assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be

accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third

parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.

Outline Dimension

Dim ensions In Millimet ers Dimensions 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 2.950 3.050 0.116 0.120

D2 2.300 2.650 0.091 0.104

E 2.950 3.050 0.116 0.120

E2 1.400 1.750 0.055 0.069

e 0.450 0.018

L 0.350 0.450

0.014 0.018

W-Type 12L DFN 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