Richtek RT8020AGQW, RT8020APQW, RT8020BGQW, RT8020BPQW, RT8020CGQW Schematic [ru]

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RT8020

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

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 R

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.

dramatically reduces conduction

DS(ON)

Features



2.5V to 5.5V Input Range





 Adjustable Output From 0.6V to V



 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



Applications

 Mobile Phones

 Personal Information Appliances

 Wireless and DSL Modems

 MP3 Players

 Portable Instruments

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.

Pin Configurations

(TOP VIEW)

GND

EN2

NC2

FB2

GND

LX1

VIN1

VIN2

LX2

GND

FB1

NC1

EN1

WDFN-12L 3x3

Ordering Information

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.

DS8020-06 March 2012 www.richtek.com

RT8020

(

)

Marking Information

RT8020APQW

C2- : Product Code

C2-YM

DNN

YMDNN : Date Code

RT8020CPQW

C4-YM

DNN

C4- : Product Code

YMDNN : Date Code

RT8020AGQW

C2=YM

DNN

RT8020BPQW

C3-YM

DNN

RT8020BGQW

C3=YM

DNN

C2= : Product Code

YMDNN : Date Code

C3- : Product Code

YMDNN : Date Code

C3= : Product Code

YMDNN : Date Code

RT8020CGQW

C4=YM

DNN

RT8020DPQW

C5-YM

DNN

RT8020DGQW

C5=YM

DNN

C4= : Product Code

YMDNN : Date Code

C5- : Product Code

YMDNN : Date Code

C5=: Product Code

YMDNN : Date Code

Typical Application Circuit

2.2µH

IN2

4.7µF 3, Exposed Pad (13)

R12

C11 22pF

OUT1

Rx1

1 VV

REFOUTx

+×=

Rx2

R11 850k

OUT1

4.7µF

VIN2

LX2

GND

FB1

NC1

EN1

RT8020

2.2µH

EN2

NC2

FB2

GND

LX1

VIN1

Figure 1. Adjustable Voltage Regulator

OUT2

4.7µF

R21 850k

IN1

4.7µF

OUT2

C21

22pF

R22

IN1

DS8020-06 March 2012www.richtek.com

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

OUTx

IN2

4.7µF

3, Exposed Pad (13)

OUT1

4.7µF

2.2µH

RT8020

OUT1

VIN2

LX2

GND

FB1

NC1

EN1

2.2µH

EN2

NC2

FB2

GND

LX1

VIN1

Figure 2. Fixed Voltage Regulator

IN1

4.7µF

IN1

OUT2

4.7µF

RT8020

OUT2

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)

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). V

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). V

GND

Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

EN1

EN2

≦ V

IN1.

IN2.

DS8020-06 March 2012 www.richtek.com

RT8020

Function Block Diagram

ENx VINx

FBx

Slope

Compensation

Error

Amplifier

COMP

OSC and

Shutdown

Control

Current

Sense

PWM

Comparator

UVLO and

Power Good

Detector

Current Limit

Detector

Control

Logic

REF

Driver

RS1

LXx

RS2

GND

DS8020-06 March 2012www.richtek.com

Absolute Maximum Ratings (Note 1)

RT8020

 Supply Input Voltage, V

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

 Power Dissipation, P

, V

IN1

IN2

@ TA = 25°C

---------------------------------------------------------------------------------- −0.3V to 6.5V

+ 0.3V)

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

Recommended Operating Conditions (Note 4)

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

 Junction Temperature Range ---------------------------------------------------------------------------------------

 Ambient Temperature Range ---------------------------------------------------------------------------------------

−40°C to 125°C

−40°C to 85°C

Electrical Characteristics

(VIN = 3.6V, V

= 2.5V, V

OUT

= 0.6V, L = 2.2uH, CIN = 4.7μF, C

REF

= 10μF, T

OUT

= 25°C, I

= 1A unless otherwise specified)

MAX

Parameter Symbol Test Conditions Min Typ Max Unit

Channel 1 and Channel 2

Input Voltage Range

Under Voltage Lock Out threshold

UVLO -- 1.8 -- V

2.5 -- 5.5 V

Hysteresis -- 0.1 -- V

Quiescent Current

Shutdown Current

Reference Voltage

Adjustable Output Voltage Range

Output Voltage Accuracy

Fix

SHDN

REF

OUT

ΔV

OUT

OU T

EN = GND -- 0.1 1

For Adjustable Output Voltage 0.588 0.6 0.612 V

(Note 6)

0A < I

0A < I V

OUT

= 0mA, VFB = V

= 2.5V to 5.5V, V

< 1A

OUT

= 2.5V to 5.5V, V

< 1A

OUT

= 2.5 to 5.5V, V

< 1A

OUT

= V

+ ΔV to 5.5V (Note 5)

OUT

= 2.5V, 0A < I

= V

+ ΔV to 5.5V (Note 5)

OUT

= 3.3V, 0A < I

REF

OUT

OU T

+ 5%

= 1.2V

= 1.3V

= 1.8V

< 1A

-- 50 70 μA μA

REF

−3

−ΔV

-- 3 %

−3 -- 3 %

−3

-- 3 %

DS8020-06 March 2012 www.richtek.com

RT8020

Parameter Symbol Test Conditions Min Typ Max Unit

Output Voltage Accuracy

Adjustable ΔV

OUT

FB Input Current IFB V

P-Channel Current Limit I

EN Input Voltage

Oscillator Frequency f

Thermal Shutdown Temperature T

of P-MOSFET R

DS(ON)

of N-MOSFET R

DS(ON)

Logic-High V

Logic-Low V

DS(ON)_P

DS(ON)_N

LIM_P

VIN = 2.5V to 5.5V 1.5 -- VIN

EN_H

VIN = 2.5V to 5.5V -- -- 0.4

EN_L

OSC

-- 160 -- °C

= V

0A < I

= VIN −50 -- 50 nA

OUT

= 2.5V to 5.5 V 1.4 1.5 -- A

= 3.6V, I

+ ΔV to 5.5V (Note 5)

OUT

< 1A

OUT

= 200mA

= 100mA 1.2 1.5 1.8 MHz

OUT

−3 -- 3 %

= 2.5V -- 0.38 --

= 3.6V -- 0.28 --

= 2.5V -- 0.35 --

= 3.6V -- 0.25 --

Maximum Duty Cycle 100 -- -- %

LX Leakage Current ILX V

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

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 = I Note 6. Guarantee by design.

is measured at T

measured at the exposed pad of the package.

x P

OUT

RDS(ON)

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

= 3.6V, V

= 0V or V

= 3.6V −1 -- 1 μA

DS8020-06 March 2012www.richtek.com

Typical Operating Characteristics

RT8020

Efficiency vs. Output Current

100

VIN = 3.6V

VIN = 4.2V

VIN = 5.0V

Efficiency (%)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

= 3.3V, L = 4.7μH, C

OUT

Output Current (A)

Efficiency vs. Output Current

100

Efficiency (%)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

= 1.2V, L = 2.2μH, C

OUT

Output Current (A)

= 4.7μF

OUT

VIN = 5.0V

VIN = 3.6V

VIN = 3.3V

VIN = 2.5V

= 10μF

OUT

Efficiency vs. Output Current

100

Efficiency (%)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

= 1.2V, L = 4.7μH, C

OUT

Output Current (A)

UVLO Threshold vs. Temperature

2.00

1.90

1.80

1.70

1.60

1.50

1.40

UVLO Threshold (V)

1.30

1.20

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

Temperature

Rising

Falling

OUT

(°C)

= 1.2V, I

VIN = 5.0V

VIN = 3.6V

VIN = 3.3V

VIN = 2.5V

= 4.7μF

OUT

= 0A

OUT

EN Pin Threshold vs. Input Voltage

1.20

1.15

1.10

1.05

1.00

0.95

0.90

0.85

0.80

0.75

EN Pin Threshold (V)

0.70

0.65

0.60

2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5

Rising

Falling

OUT

= 1.2V, I

OUT

= 0A

Input Voltage (V)

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

EN Pin Threshold (V)

0.6

0.5

0.4

EN Pin Threshold vs. Temperature

Rising

Falling

VIN = 3.6V, V

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

Temperature

OUT

(°C)

= 1.2V, I

OUT

= 0A

DS8020-06 March 2012 www.richtek.com

RT8020

Output Voltage (V)

Output Voltage vs. Loading Current

1.230

1.225

1.220

1.215

1.210

1.205

1.200

1.195

1.190

1.185

1.180 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

VIN = 5.0V

VIN = 3.6V

Loading Current (A)

Switching Frequency vs . Input Voltage

1.60

1.55

1.50

1.45

Output Voltage vs. Temperature

1.25

1.24

1.23

1.22

1.21

1.20

1.19

1.18

Output Voltage (V)

1.17

1.16

1.15

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

Temperature

VIN = 3.6V, I

(°C)

Switching Frequency vs. Temperature

1.6

1.55

1.5

1.45

OUT

= 0A

1.40

1.35

Frequency(kHz)

1.30

1.25

1.20

VIN = 3.6V, V

2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5

OUT

= 1.2V, I

OUT

Input Voltage (V)

Output Current Limit vs. Input Voltage

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

1.5

Output Current Limit (A)

1.4

1.3

2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5

Input Voltage (V)

OUT

= 1.2V @ T

= 300mA

= 25°C

1.4

1.35

Frequency(kHz)

1.3

1.25

1.2

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

VIN = 3.6V, V

Temperature

OUT

(°C)

= 1.2V, I

OUT

Output Current Limit vs. Tempe rature

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

Output Current Limit (A)

1.5

1.4

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

VIN = 5.0V

VIN = 3.6V

VIN = 3.3V

Temperature

(°C)

= 300mA

= 1.2V

OUT

DS8020-06 March 2012www.richtek.com

RT8020

(2V/Div)

OUT

(1V/Div)

(500mA/Div)

(2V/Div)

VIN = 3.6V, V

Power On from EN

= 1.2V, I

OUT

Time (100μs/Div)

OUT

= 10mA

Power On from V

= 1.2V, I

OUT

= 10mA

Power On from EN

VIN = 3.6V, V

(2V/Div)

OUT

(1V/Div)

(500mA/Div)

VIN = 3.6V, V

(2V/Div)

= 1.2V, I

OUT

= 1A

Time (100μs/Div)

Power Off from EN

= 1.2V, I

OUT

= 10mA

OUT

(1V/Div)

(1A/Div)

OUT

(50mV/Div)

OUT

(500mA/Div)

Time (250μs/Div)

Load Transient Response

VIN = 3.6V, V

= 1.2V, I

OUT

= 50mA to 1A

OUT

(1V/Div)

(1A/Div)

OUT

(50mV/Div)

OUT

(500mA/Div)

Time (100μs/Div)

Load Transient Response

VIN = 3.6V, V

OUT

= 1.2V, I

OUT

= 50mA to 0.5A

Time (50μs/Div)

DS8020-06 March 2012 www.richtek.com

RT8020

OUT

(50mV/Div)

OUT

(500mA/Div)

OUT

(10mV/Div)

Load Transient Response

VIN = 5.0V, V

= 1.2V, I

OUT

Time (50μs/Div)

Ripple

VIN = 3.6V, V

= 1.2V, I

OUT

= 50mA to 1A

= 1A

OUT

(50mV/Div)

OUT

(500mA/Div)

OUT

(10mV/Div)

Load Transient Response

VIN = 5.0V, V

= 1.2V, I

OUT

Time (50μs/Div)

OUT

Ripple

VIN = 5.0V, V

= 1.2V, I

OUT

= 50mA to 0.5A

= 1A

(2V/Div)

Time (500ns/Div)

(2V/Div)

Time (500ns/Div)

DS8020-06 March 2012www.richtek.com

Applications Information

RT8020

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 C

OUT

Inductor Selection

For a given input and output voltage, the inductor value

and operating frequency determine the ripple current. The

ripple current ΔI

increases with higher VIN and decreases

with higher inductance.

ΔI

⎡

⎢

⎣

⎤ ⎥

⎦

⎡

−×

⎢

⎣

⎤

OUTOUT

⎥

⎦

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(I

). The largest ripple current occurs at the

MAX

highest VIN. To guarantee that the ripple current stays

below a specified maximum, the inductor value should be

chosen according to the following equation :

⎡

L(MAX)

⎤ ⎥

⎦

−×

⎢

IN(MAX)

⎣

⎡

OUT

⎢

Δ×

⎣

OUT

⎤ ⎥

⎦

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 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 C

Selection

OUT

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 :

OUT(MAX)RMS

OUT

This formula has a maximum at VIN = 2V

RMS

= I

/2. This simple worst-case condition is

OUT

−=

OUT

, where

OUT

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 C

is determined by the effective series

OUT

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, ΔV

⎡

ESR ΔIΔV

LOUT

⎢

⎣

, is determined by :

OUT

⎤

+≤

8fC

OUT

⎥

⎦

DS8020-06 March 2012 www.richtek.com

RT8020

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.

OUT

RT8020

GND

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 :

= V

OUT

Where V

x (1+ R1/R2)

REF

is the internal reference voltage (0.6V typical)

REF

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 V

to ground.

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

larger than the DC bias current. In continuous mode,

GATECHG

= 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

DS8020-06 March 2012www.richtek.com

RT8020

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 R

and the duty cycle (DC) is shown as

DS(ON)

follows :

RSW = R

The R

DS(ON)

DS(ON)TOP

x DC + R

DS(ON)BOT

x (1 − DC)

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 R

and multiply the result by the square of the average output

current. Other losses including CIN and C

OUT

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 :

Where T

D(MAX)

= ( T

J(MAX)

− TA ) / θ

J(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 T

is the maximum junction temperature of

J(MAX)

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

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 :

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

D(MAX)

WDFN-12L 3x3 packages

The maximum power dissipation depends on operating

ambient temperature for fixed T

and thermal

J(MAX)

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.

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

Maximum Power Dissipation (W)

0.0 0 25 50 75 100 125

Four-Layer PCB

Ambient Temperature (°C)

Figure 4. De-rating Curves for RT8020 Package

Checking Tra n 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, V

equal to ΔI

resistance of C

discharge C

(ESR), where ESR is the effective series

LOAD

OUT

generating a feedback error signal used

OUT

by the regulator to return V

During this recovery time, V

immediately shifts by an amount

OUT

. ΔI

also begins to charge or

LOAD

to its steady-state value.

OUT

can be monitored for

OUT

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.

DS8020-06 March 2012 www.richtek.com

RT8020

Table 1. Recommended Inductors

Component

Supplier

T AIYO YUDEN NR 3015 2.2 60 1480 3 x 3 x 1.5 T AIYO 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 GTSD32 2.2 58 1500 3.85 x 3.85 x 1.8 GOTREND GTSD32 4.7 146 1 100 3.85 x 3.85 x 1. 8

Series

Inductance

(μH)

DCR

(mΩ)

Current Rati ng

(mA)

Dimensions

(mm)

Table 2. Recomm ended Capacitors for CIN and C

Compon ent Sup pl ie r Part No. Capacit ance (μF) Case Size

TDK C1608JB0J475M 4.7 0603

TDK C2012JB0J106M 10 0805 MURAT A GRM188R60J475KE19 4.7 0603 MURAT A GRM219R60J106ME19 10 0805

TAIYO YUDEN JMK107BJ475RA 4.7 0603 TAIYO YUDEN JMK107BJ106MA 10 0603 TAIYO YUDEN JMK212BJ106RD 10 0805

OUT

DS8020-06 March 2012www.richtek.com

Outline Dimension

RT8020

DETAIL A

Pin #1 ID a nd T ie Bar Mark Option s

Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated.

Dimensions In Millimeters Dimension s 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

W-Type 12L DFN 3x3 Package

0.014 0.018

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.

DS8020-06 March 2012 www.richtek.com

Richtek RT8020AGQW, RT8020APQW, RT8020BGQW, RT8020BPQW, RT8020CGQW Schematic [ru]

Specifications and Main Features

Frequently Asked Questions

User Manual