Richtek RT8813AGQW Schematic [ru]

Download

RT8813A

Multi-Phase PWM Controller with PWM-VID Reference

General Description

The RT8813A is a 3/2/1 phase synchronous Buck PWM

controller which is optimized for high performance graphic

microprocessor and computer applications. The IC

integrates a Constant-On-Time (COT) PWM controller, two

MOSFET drivers with internal bootstrap diodes, as well

as channel current balance and protection functions

including Over Voltage Protection (OVP), Under Voltage

Protection (UVP), current limit, and thermal shutdown into

the WQFN-24L 4x4 package.

The RT8813A adopts R

Current limit is accomplished through continuous inductor-

current-sense, while R

accurate channel current balance. Using the method of

current sampling utilizes the best advantages of each

technique.

The RT8813A features external reference input and PWM-

VID dynamic output voltage control, in which the feedback

voltage is regulated and tracks external input reference

voltage. Other features include adjustable switching

frequency, dynamic phase number control, internal/external

soft-start, power good indicator, and enable functions.

current sensing technique.

DS(ON)

current sensing is used for

DS(ON)

Features



Multi-Phase PWM Controller





 Two Embedded MOSFET Drivers and Embedded



Switching Boot Diode



 External Reference Input Control



 PWM-VID Dynamic Voltage Control



 Dynamic Phase Number Control



 Lossless R



 Internal Fixed and External Adjustable Soft-Start



 Adjustable Current Limit Threshold



 Adjustable Switching Frequency



 UVP/OVP Protection



 Shoot Through Protection and Short Pulse Free



Technology



 Support an Ultra-Low Output Voltage as Standby



Voltage



 Thermal Alert Indicator in 2/1 Active Phase



Application



 Thermal Shutdown



 Power Good Indicator



 RoHS Compliant and Halogen Free



Current Sensing for Current Balance

DS(ON)

Simplified Application Circuit

VCC/ISEN1

BOOT1

RT8813A

UGATE1

PHASE1

LGATE1

TALERT/ISEN2

BOOT2

UGATE2

PHASE2

LGATE2

RGND

VSNS

PWM3

GND

SEN1

SEN2

Driver

PWM PHASE

GND

VCC

GND_SNS

OUT_SNS

OUT

PVCC

SET3

PVCC

TON

PGOOD

PSI

VID

TSEN/ISEN3

PVCC

TON

PGOOD

PSI

VID

Chip Enable

DS8813A-05 December 2013 www.richtek.com

RT8813A

Applications

 CPU/GPU Core Power Supply

 Notebook PC Memory Power Supply

 Chipset/RAM Power Supply

 Generic DC/DC Power Regulator

Ordering Information

RT8813A

Package Type QW : WQFN-24L 4x4 (W-Type) (Exposed Pad-Option 1)

Lead Plating System G : Green (Halogen Free and Pb Free)

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.

Function Pin Description

Marking Information

0P= : Product Code

0P=YM

YMDNN : Date Code

DNN

Pin Configurations

(TOP VIEW)

PVCC

LGATE1

PWM3

LGATE2

21 20 1924 2223

GND

TON

VREF

VSNS

RGND

WQFN-24L 4x4

BOOT1

UGATE1

EN PSI VID

REFADJ

PHASE1

78910 1211

REFIN

PHASE2

BOOT2

UGATE2

PGOOD

VCC/ISEN1

TALERT/ISEN2

TSNS/ISEN3

Pin No. Pin Name Pin Function

1 BOOT1 Bootstrap Suppl y for PWM 1. This pin powers the high side MOSFE T driver.

2 UGATE1

High Side Gate Driver of PWM 1. This pin prov ides the gate drive for the converter's high side MOSFET. Connect this pin to the Gate of high s ide MOSFET.

3 EN Enable Contro l I nput. Active hig h input.

Power Saving Interface. When the voltage is pulled below 0.8V, the device will operate

4 PSI

into 1 phase DEM. When the voltage is bet ween 1.2V to 1.8V, the dev ice will operate into 1 phase f orce CCM. W hen t he voltage is between 2.4V to 5 .5V, the device will operate into active phase force CCM (only for 2 or 3 phase).

5 VID

Programming Output Voltage Contr ol Input. Ref er to PWM-VID Dynamic Voltage Control .

6 REFADJ Refere nce Ad justment Output. Refer t o PWM-VID Dynamic Voltage Contro l.

7 REF IN External Reference Input.

8 VREF

9 TON

Refere nce Voltage Output. This is a high precision voltage refere nce (2V ) from VREF pin to RGND pi n.

On-Time/ Switching Freq uency Adjustment Input. Connect a 100pF capacito r between C

and gr ound is optional for noise imm unity enhancem ent.

TON

10 RGND Negative Remote Sense Input. Connect this pin to the ground of output lo ad.

11 V SNS Positive Remote Sense Input. Connect t his pin to the positive terminal of output load.

12 SS

Soft-Start Time Sett in g. Connect an ext erna l capacitor to adjust soft -start time. When the ex ternal capacitor is remove d, t he i nt ernal soft-start function will be chose.

TSNS Temperatu re Sensing Inp ut f or 2/1 Phase Operati on.

ISEN3 Phase 3 Current Sense Inp ut f or 3 Phase Operation.

DS8813A-05 December 2013www.richtek.com

Pin No. Pin Name Pin Function

RT8813A

16 PGOOD Power Good Indicator Output. Active high open drain output.

17 UGATE2

18 BOOT2 Bootstrap Supply for of PWM 2. This pin powers the high side MOSFET driver.

19 PHASE2

20 LG ATE2

21 PVCC

22 PW M 3

23 LG ATE1

24 PHASE1

25 (Exposed Pad) GND

TALERT

ISEN2 Phase 2 Current Sense Input for 3 Phase Operation.

VCC Supply Voltage Input for 2/1 Phase Operation. (Connect to PVCC)

ISEN1 Phase 1 Current Sense Input for 3 Phase Operation. (Connect to PHASE1)

Thermal Alert. Active low open drain output for 2/1 Phase Operation.

High Side Gate Driver of PWM 2. This pin provides the gate drive for the converter's high side MOSFET. Connect this pin to the Gate of high side MOS FET.

Switch Node for PWM2. This pin is return node of the high side driver of PWM

2. Connect this pin to the Source of high side MOSFET together with the Drain of low side MOSFET and the inductor.

Low Side Gate Driver of PWM 2. This pin provides the gate drive for the converter's low side MOSFET. Connect this pin to the Gate of low side MOS FET.

Supply Voltage Input. Connect this pin to a 5V bias supply. Place a high quality bypass capacitor from this pin to GND.

Third Phase PWM Control Signal Output to Driver for 3 Phase Operation. In 2/1 Phase Operation, this pin is high impedance.

Low Side Gate Driver of PWM 1. This pin provides the gate drive for the converter's low side MOSFET. Connect this pin to the Gate of low side MOS FET.

Switch Node for PWM1. This pin is return node of the high side driver of PWM

1. Connect this pin to the Source of high side MOSFET together with the Drain of low side MOSFET and the inductor.

Ground. The Exposed pad should be soldered to a large PCB and connected to GND for maximum thermal dissipation.

DS8813A-05 December 2013 www.richtek.com

RT8813A

Function Block Diagram

VREF

VID

REFADJ

PSI

REFIN

OV Threshold

Select

40% REFIN

Mode Select

Reference

Output Gen.

Power On Reset

& Central Logic

Control & Protection Logic

Boot-Phase Detection 1

PVCC

PGOOD

VSNS

RGND

TON

VCC/

ISEN1

TALERT/

ISEN2

TSNS/ ISEN3

Soft-Start

& Slew Rate

Control

Enable

Logic

To Power On Reset

VIN

Detection

Phase Select

Internal

OTP

To Central Logic

PWM

CMP

To Driver Logic To Power On Reset

To Protection Logic

ZCDPHASE1

TON

Gen 1

TON

Gen 2

TON

Gen 3

To Driver Logic

Current

Balance

Current

Limit

Boot-Phase Detection 2

PWM1

Driver

Logic

PWM2

S/H

ISEN3

BOOT1 UGATE1 PHASE1

LGATE1

BOOT2 UGATE2

PHASE2

LGATE2

PWM3

DS8813A-05 December 2013www.richtek.com

Operation

RT8813A

The RT8813A is a 3/2/1 phase synchronous Buck PWM

controller with integrated drivers which are optimized for

high performance graphic microprocessor and computer

applications. The IC integrates a COT (Constant-On-Time)

PWM controller with two MOSFET drivers, as well as

output current monitoring and protection functions.

Referring to the function block diagram of TON Genx, the

synchronous UGATE driver is turned on at the beginning

of each cycle. After the internal one-shot timer expires,

the UGATE driver will be turned off. The pulse width of

this one-shot is determined by the converter's input voltage

and the output voltage to keep the frequency fairly constant

over the input voltage range and output voltage. Another

one-shot sets a minimum off-time.

The RT8813A also features a PWM-VID dynamic voltage

control circuit driven by the pulse width modulation

method. This circuit reduces the device pin count and

enables a wide dynamic voltage range.

Soft-Start (SS)

For internal soft-start function, an internal current source

charges an internal capacitor to build the soft-start ramp

voltage. The output voltage will track the internal ramp

voltage during soft-start interval. For external soft-start

function, an additional capacitor connected from SS to

the GND will be charged by a current source and

determines the soft-start time.

Current Limit

The current limit circuit employs a unique “valley” current

sensing algorithm. If the magnitude of the current sense

signal at PHASE is above the current limit threshold, the

PWM is not allowed to initiate a new cycle. Thus, the

current to the load exceeds the average output inductor

current, the output voltage falls and eventually crosses

the under voltage protection threshold, inducing IC

shutdown.

Over Voltage Protection (OVP) & Under Voltage Protection (UVP)

The output voltage is continuously monitored for over

voltage and under voltage protection. When the output

voltage exceeds its set voltage threshold (If V

OV = 2V, or V

> 1.33V, OV = 1.5 x V

REFIN

≤ 1.33V,

), UGATE

goes low and LGATE is forced high; when it is less than

40% of its set voltage, under voltage protection is triggered

and then both UGATE and LGATE gate drivers are forced

low. The controller is latched until PVCC is re-supplied

and exceeds the POR rising threshold voltage or EN is

reset.

PGOOD

The power good output is an open drain architecture.

When the soft-start is finished, the PGOOD open drain

output will be high impedance.

Current Balance

The RT8813A implements internal current balance

mechanism in the current loop. The RT8813A senses per

phase current and compares it with the average current. If

the sensed current of any particular phase is higher than

average current, the on-time of this phase will be adjusted

to be shorter.

DS8813A-05 December 2013 www.richtek.com

RT8813A

Absolute Maximum Ratings (Note 1)

 TON to GND ------------------------------------------------------------------------------------------------------------------ −0.3V to 30V

 RGND to GND --------------------------------------------------------------------------------------------------------------- −0.7V to 0.7V

 BOOTx to PHASEx -------------------------------------------------------------------------------------------------------- −0.3V to 6V

 PHASEx to GND

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 30V

<20ns ------------------------------------------------------------------------------------------------------------------------- −8V to 36V

 UGATEx to PHASEx

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V

<20ns ------------------------------------------------------------------------------------------------------------------------- −5V to 7.5V

 LGATEx to GND

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V

<20ns ------------------------------------------------------------------------------------------------------------------------- −2.5V to 7.5V

 Other Pins-------------------------------------------------------------------------------------------------------------------- −0.3V to 6V

 Power Dissipation, P

WQFN-24L 4x4 ------------------------------------------------------------------------------------------------------------- 3.57W

 Package Thermal Resistance (Note 2)

WQFN-24L 4x4, θJA-------------------------------------------------------------------------------------------------------- 28°C/W

WQFN-24L 4x4, θJC------------------------------------------------------------------------------------------------------- 7°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 Model)----------------------------------------------------------------------------------------------- 2kV

@ T

= 25°C

Recommended Operating Conditions (Note 4)

 Input Voltage, V

 Supply Voltage, V

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

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

----------------------------------------------------------------------------------------------------------- 7V to 26V

---------------------------------------------------------------------------------------------------- 4.5V to 5.5V

PVCC

Electrical Characteristics

= 25°C unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

PWM Controller

PVCC Supply Voltage V

PVCC Supply Current I

PVCC Shutdown Current I

PVCC POR Threshold 3.8 4.1 4.4 V

POR Hysteresis -- 0.3 -- V

4.5 -- 5.5 V

PVCC

SUPPLY

SHDN

EN = 3.3V, Not Switching -- 1.5 2 mA

EN = 0V -- -- 10 A

DS8813A-05 December 2013www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Unit

Switching Frequ ency fSW R

Minimum On-Time t

Minimum Off-Time t

ON(MIN)

OFF(MI N)

-- 70 -- ns

= 500k (Note 5) 270 300 330 k Hz

TON

-- 300 -- ns

EN Threshold

RT8813A

EN Input Voltage

Logic-High V

Logic-Low V

1.6 -- -- V

ENH

-- -- 0.8 V

ENL

Mode Decision

PSI High Threshold V

PSI In termediate Thr eshold V

PSI Low Threshold V

Logic-High V

VID Input Voltage

Logic-Low V

Enables Two Phases with FCCM 2.4 -- -- V

PSIH

Enables One Phases with FCCM 1.2 -- 1.8 V

PSIM

Enables One Phases with DEM -- -- 0.8 V

PSIL

2 -- -- V

VIDH

-- -- 1 V

VIDL

Protection Function

Zero Current Crossing Threshold

Current Limit Setting Current I

Current Limit Setting Current Temperature Coef ficient

8 -- 8 mV

9 10 11 A

OCSET

OCSET_TC

-- 6300 -- ppm/C

Current Limit Threshold R

Absolute Over Voltage Prote ction Threshold

Relative Over Voltage Prote ction Threshold

OVP, Absolute

OVP, Relative VRE FIN

= 10k -- 60 -- mV

OCSET

 1.33V 1.9 2 2.1 V

RE FIN

> 1.33V 145 150 155 %

OV Fault Delay FB forced above OV th resh old -- 5 -- s

Relative Under Voltage Prote ction Threshold

UVP 35 40 45 %

UVP

UV Fault Delay FB forced above UV threshol d -- 3 -- s

Thermal Shutdown Th reshold TSD -- 150 -- C

Minim um TM Threshold V

PGOOD Blanking Time (Interna l)

(No Shutting Do wn) 0.98 1 1.02 V

TSEN

From EN = high to PGOOD = high with VSNS withi n regulation poin t

-- 2.5 -- ms

From first UGATE to VSNS

VSNS Soft-Start (Internal)

regulation point, V

RE FIN

= 1V and

-- 0.7 -- ms

VSNS initial = 0 V

Soft-Start Current Source ISS -- 5 -- A

Er ror Amp l if ier

VSNS Error Comparator Threshold (Valley)

= 1V 17.5 12.5 7.5 mV

RE FIN

DS8813A-05 December 2013 www.richtek.com

RT8813A

Parameter Symbol Test Conditions Min Typ Max Unit

Refer ence

Reference Voltage V

Driver On-Resi s tance

VREF

Sourcing Current = 1mA, VID no Switching

1.98 2 2.02 V

UGATE Driver Source R

UGATE Driver Sink R

LGATE Driver Source R

LGATE Driver Sink R

UGATEsr

UGATEsk

LGATEsr

LGATEsk

BOOT x  PHASEx Forced to 5V -- 2 4 

BOOT x  PHASEx Forced to 5V -- 1 2 

LGATEx, High State -- 1.5 3 

LGATEx, Low State -- 0.7 1.5 

From LGATE Falling to UGATE Rising -- 30 --

Dead-Time

From UGATE Falling to LGATE Rising -- 20 --

Internal Boost Charging Switch On-Resistance

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 is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Not production tested. Test condition is V

is measured at T

measured at the exposed pad of the package.

PVCC to BOOTx, I

BOOT

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

= 8V, V

OUT

= 1V, I

= 10mA -- 40 80 

BOOT

= 20A using application circuit.

OUT

DS8813A-05 December 2013www.richtek.com

Typical Application Circuit

500k

REF1

20k

BOOT

TON

Optional

PGOOD

Enable

RGND

PHASE1

PHASE2

PHASE3

PSI

VID

RGND

REF2

0.1µF

REFADJ

2.7nF

RGND

2.2µF

100k

REFADJ

20k

10k

TON

REFIN

STANDBY

PVCC

2.2

1µF

STANDBY

5.1k 18k NC

RGND

PVCC

TON

PGOOD

PSI

VID

VREF

REFADJ

REFIN

VCC/ISEN1

TALERT/ISEN2

TSEN/ISEN3

BOOT1

RT8813A

UGATE1

PHASE1

LGATE1

BOOT2

UGATE2

PHASE2

LGATE2

GND

25 (Exposed pad)

RGND

VSNS

PWM3

0.1µF

OCSET

10k

C 47pF

0.1µF

PVCC

Driver Enable

RT8813A



330µF 2V x 4

470µF/50V x 2

22µF x 15

1010

GND_SNS

OUT_SNS

0.36µH/1.05m

OUT



10µF x 6

0.36µH/1.05m



0.1µF

2.2

BOOT UGATE

RT9610

PWM

PHASE

VCC

LGATE

GND

STANDBY

Figure 1. 3 Active Phase Configuration

0.36µH/1.05m

10µF x 4

0.36µH/1.05m



470µF/50V x 2



330µF 2V x 4

1010

22µF x 15

GND_SNS

OUT_SNS

OUT

PSI

VID

5 22

0.1µF

R 10k

OCSET

47pF

PSI

VID

TON

500k

PVCC

2.2

1µF

Optional

PGOOD

Enable

0.1µF

RGND

REFADJ

2.7nF

RGND

REF2

18k NC

RGND

PVCC

OTSET

STANDBY

5.1k

REF1

BOOT

RGND

20k

RGND

10k

2.2µF

100k

REFADJ

20k

100k

TON

R 10k

REFIN

NTC

PVCC

TON

PGOOD

VREF

REFADJ

REFIN

VCC/ISEN1

TALERT/ISEN2

TSEN/ISEN3VREF

BOOT1

RT8813A

UGATE1

PHASE1

LGATE1

BOOT2

UGATE2

PHASE2

LGATE2

RGND

VSNS

PWM3

GND

25 (Exposed pad)

Figure 2. 2 Active Phase Configuration

DS8813A-05 December 2013 www.richtek.com

RT8813A

2.2

STANDBY

5.1k 18k NC

STANDBY

RGND

PVCC

1µF

REF1

20k

BOOT

TON

500k

RGND

Optional

Enable

RGND

REF2

PVCC

OTSET

0.1µF

REFADJ

2.7nF

RGND

100k

10k

2.2µF

TON

100k

REFADJ

20k

REFIN

R 10k

PVCC

TON

PGOODPGOOD

VREF

REFADJ

REFIN

VCC/ISEN1

TALERT/ISEN2

TSEN/ISEN3VREF

NTC

BOOT1

RT8813A

UGATE1

PHASE1

LGATE1

RGND

BOOT2

UGATE2

PHASE2

LGATE2

GND

25 (Exposed pad)

VSNS

PSI

VID

PWM3

0.1µF

R 10k

47pF

PSI

VID

OCSET

Floating

10µF x 4 470µF/50V x 2

0.36µH/1.05m



330µF 2V x 4

1010

22µF x 15

GND_SNS

OUT_SNS

OUT

Figure 3. 1 Active Phase Configuration

DS8813A-05 December 2013www.richtek.com

Typical Operating Characteristics

RT8813A

(ns)

Efficiency (%)

Efficiency vs. Load Current

100%

100

90%

80%

70%

60%

50%

40%

30%

20%

10%

0 5 10 15 20 25 30 35 40 45 50 55 60

VIN = 19V, V

= 0.9V, 2 Phase Operation

OUT

Load Current (A)

TON vs. Temperature

185.0

182.5

180.0

177.5

175.0

172.5

PVCC

= 5V,

Efficiency vs. Load Current

100%

100

90%

80%

70%

60%

50%

40%

Efficiency (%)

30%

20%

10%

0.01 0.1 1 10

= 0.9V, 1 Phase with DEM Operation

OUT

Load Current (A)

vs. Temperature

2.04

2.03

2.02

2.01

(V)

2.00

REF

1.99

REF

VIN = 19V, V

PVCC

= 5V,

170.0

167.5

165.0

VIN = 19V, V

-50 -25 0 25 50 75 100 125

= 5V, No Load

PVCC

Temperature (°C)

Inductor Current vs. Output Current

Inductor Current (A)

0 102030405060

Phase 1

Phase 2

VIN = 19V, V

Output Current (A)

PVCC

= 5V

1.98

1.97

1.96

(5V/Div)

OUT

(1V/Div)

UGATE1

(50V/Div)

UGATE2

(50V/Div)

VIN = 19V, V

-50 -25 0 25 50 75 100 125

= 5V, No Load

PVCC

Temperature (°C)

Power On from EN

VIN = 19V, V

Time (1ms/Div)

PVCC

= 5V, I

OUT

= 50A

DS8813A-05 December 2013 www.richtek.com

RT8813A

(5V/Div)

OUT

(1V/Div)

UGATE1

(50V/Div)

UGATE2

(50V/Div)

PVCC

(5V/Div)

Power Off from EN

VIN = 19V, V

Time (1ms/Div)

PVCC

= 5V, I

Power Off from VCC

OUT

= 50A

PVCC

(5V/Div)

OUT

(1V/Div)

UGATE1 (50V/Div)

UGATE2 (50V/Div)

DVID

(2V/Div)

Power On from VCC

VIN = 19V, V

Time (1ms/Div)

PVCC

= 5V, I

OUT

Dynamic Output Voltage Control

VIN = 19V, V

PVCC

= 5V

= 50A

OUT

(1V/Div)

UGATE1

(50V/Div)

UGATE2

(50V/Div)

DVID

(2V/Div)

OUT

(1V/Div)

UGATE1

(50V/Div)

UGATE2

(50V/Div)

VIN = 19V, V

PVCC

= 5V, I

OUT

= 50A

Time (1ms/Div)

Dynamic Output Voltage Control

OUT

VIN = 19V, V

= 50A, V

= 1.2V to 0.6V

REFIN

PVCC

= 5V

OUT

(1V/Div)

UGATE1 (50V/Div)

UGATE2 (50V/Div)

OUT

(100mV/Div)

OUT

(50A/Div)

UGATE2

(50V/Div)

UGATE1

(50V/Div)

= 50A, V

OUT

= 0.6V to 1.2V

REFIN

Time (50μs/Div)

Load Transient Response

VIN = 19V, V

PVCC

= 5V

Time (50μs/Div)

Time (20μs/Div)

DS8813A-05 December 2013www.richtek.com

RT8813A

OUT

(100mV/Div)

OUT

(50A/Div)

UGATE2

(50V/Div)

UGATE1

(50V/Div)

VSNS

(1V/Div)

UGATE1

(20V/Div)

Load Transient Response

VIN = 19V, V

Time (20μs/Div)

PVCC

UVP

= 5V

VSNS

(1V/Div)

UGATE1

(20V/Div)

LGATE1 (5V/Div)

(20A/Div)

UGATE1

(50V/Div)

OVP

VIN = 19V, V

Time (100μs/Div)

PVCC

OCP

= 5V, No Load

LGATE1 (5V/Div)

VIN = 19V, V

PVCC

Time (20μs/Div)

= 5V, I

OUT

= 40A

LGATE1

(10V/Div)

VIN = 19V, V

Time (20μs/Div)

PVCC

= 5V

DS8813A-05 December 2013 www.richtek.com

RT8813A



Application Information

The RT8813A is a multi-phase synchronous Buck PWM

controller with integrated drivers which is optimized for

high-performance graphic microprocessor and computer

applications. A COT (Constant-On-Time) PWM controller

and two MOSFET drivers with internal bootstrap diodes

are integrated so that the external circuit can be easily

designed and the number of component is reduced.

The topology solves the poor load transient response timing

problems of fixed-frequency mode PWM and avoids the

problems caused by widely varying switching frequencies

in conventional constant on-time and constant off-time

PWM schemes.

The IC supports dynamic mode transition function with

various operating states, which include multi-phase with

CCM operation and single phase with diode emulation

mode. These different operating states make the system

efficiency as high as possible.

The RT8813A provides a PWM-VID dynamic control

operation in which the feedback voltage is regulated and

tracks external input reference voltage. It also features

complete fault protection functions including over voltage,

under voltage and current limit.

Remote Sense

The RT8813A uses the remote sense path (VSNS and

RGND) to overcome voltage drops in the power lines by

sensing the voltage directly at the end of GPU. Normally,

to protect remote sense path disconnecting, there are

two resistors (R

) connecting between local sense path

Local

and remote sense path. That is, in application with remote

sense, the R

no need of remote sense, the R

is recommended to be 10Ω to 100Ω. If

Local

is recommended to

Local

be 0Ω.

BOOT

UGATE

PHASE

LGATE

RGND

VSNS

Local Sense Path

OUT

+ R

Local

Remote Sense Path

Local

GPU

Figure 4. Output Voltage Sensing

PWM Operation

The RT8813A integrates a Constant-On-Time (COT) PWM

controller, and the controller provides the PWM signal

which relies on the output ripple voltage comparing with

internal reference voltage as shown in Figure 5. Referring

to the function block diagram of TON Genx, the

synchronous UGATE driver is turned on at the beginning

of each cycle. After the internal one-shot timer expires,

the UGATE driver will be turned off. The pulse width of

this one-shot is determined by the converter's input

voltage and the output voltage to keep the frequency fairly

constant over the input voltage and output voltage range.

Another one-shot sets a minimum off-time.

OUT

PEAK

OUT

VALLEY

REF

Figure 5. Constant On-Time PWM Control

On-Time Control

The on-time one-shot comparator has two inputs. One

input monitors the output voltage, while the other input

samples the input voltage and converts it to a current.

This input voltage proportional current is used to charge

an internal on-time capacitor. The on-time is the time

required for the voltage on this capacitor to charge from

zero volts to V

, thereby making the on-time of the high

OUT

side switch directly proportional to output voltage and

inversely proportional to input voltage. The implementation

results in a nearly constant switching frequency without

the need for a clock generator.

2 V 3.2p



T = R

ON TON

OUT

V0.5





And then the switching frequency FS is :

F= V V T

SOUT INON

TON

value of R



is a resistor connected from the VIN to TON pin. The

can be selected according to Figure 6.

TON

The recommend operation frequency range is 150kHz to

600kHz.

DS8813A-05 December 2013www.richtek.com

RT8813A

800

700

600

500

400

Frequency (kHz) 1

300

200

150 250 350 450 550 650 750

(k )

TON

Figure 6. Frequency vs. R

TON

Active Phase Circuit setting : Before POR

The RT8813A can operate in 3/2/1 phase. When PVCC is

higher than POR threshold and EN is higher than logic-

high level, the RT8813A will detect the VCC/ISEN1 pin to

determine how many phases should be active. For three

phases operation, the VCC/ISEN1 pin is connected to

PHASE1, the TALERT/ISEN2 pin is connected to

PHASE2, the TSNS/ISEN3 pin is connected to PHASE3,

and external MOSEFT driver's PWM pin is connected to

PWM3. For two phases operation, the VCC/ISEN1 pin is

connected to PVCC, the TALERT/ISEN2 pin is connected

to TALERT signal, the TSNS/ISEN3 pin is connected to

TSNS signal, and the PWM3 pin is connected to GND.

For one phase operation, the VCC/ISEN1 pin is connected

to PVCC, TALERT/ISEN2 pin is connected to TALERT

signal, the TSNS/ISEN3 pin is connected to TSNS signal,

the PWM3 pin is connected to GND, and UGATE2,

BOOT2, PHASE2, and LGATE 2 pins are floating. The

voltage setting at PSI pin can't higher than 1.8V.

1.2V to 1.8V, the controller will switch operation into 1

phase with force CCM. If PSI voltage is pulled between

2.4V to 5.5V, the controller will switch operation into active

phase (only for 2 or 3 phase). The operation mode is

summarized in Table 1. Moreover, the PSI pin is valid after

POR of VR.

Table 1

Operation Phase Number PSI Voltage Setting

1 phase with DEM 0V to 0.8V

1 phase with CCM 1.2V to 1.8V

Active phase with CCM 2.4V to 5.5V

Diode-Emulation Mode

In diode-emulation mode, the RT8813A automatically

reduces switching frequency at light-load conditions to

maintain high efficiency. As the output current decreases

from heavy-load condition, the inductor current is also

reduced, and eventually comes to the point that its valley

touches zero current, which is the boundary between

continuous conduction and discontinuous conduction

modes. By emulating the behavior of diodes, the low side

MOSFET allows only partial of negative current when the

inductor freewheeling current reaches negative value. As

the load current is further decreased, it takes a longer

time to discharge the output capacitor to the level that

requires the next “ON” cycle. In reverse, when the output

current increases from light load to heavy load, the

switching frequency increases to the preset value as the

inductor current reaches the continuous conduction

condition. The transition load point to the light load

operation is shown in Figure 7 and can be calculated as

follows :

(V V )



LOAD(SKIP) ON

where tON is on-time.

IN OUT



Mode Selection

The RT8813A can operate in 3 phases or 2 phases with

Slope = (V

- V

OUT

) / L

PEAK

force CCM, 1 phase with force CCM, and 1 phase with

DEM according to PSI voltage setting. If PSI voltage is

pulled below 0.8V, the controller will operate into 1 phase

LOAD

= I

PEAK/2

with DEM. In DEM operation, the RT8813A automatically

reduces the operation frequency at light load conditions

for saving power loss. If PSI voltage is pulled between

Figure 7. Boundary condition of CCM/DEM

DS8813A-05 December 2013 www.richtek.com

RT8813A

The switching waveforms may be noisy and asynchronous

in light loading diode-emulation operation condition, but

this is a normal operating condition that results in high

light-load efficiency. Trade-off in DEM noise vs. light-load

efficiency is made by varying the inductor value. Generally,

low inductor values produce a broad high efficiency range

vs. load curve, while higher values result in higher full-

load efficiency (assuming that the coil resistance remains

fixed) and less output voltage ripple. The disadvantages

for using higher inductor values include larger physical

size and degraded load-transient response (especially at

low input voltage levels).

Forced-CCM Mode

The low noise, forced-CCM mode disables the zero-

crossing comparator, which controls the low side switch

on-time. This causes the low side gate drive waveform to

be the complement of the high side gate drive waveform.

This in turn causes the inductor current to reverse at light

loads as the PWM loop to maintain a duty ratio V

OUT/VIN

The benefit of forced-CCM mode is to keep the switching

frequency fairly constant.

Soft-Start

The RT8813A provides both internal soft-start function and

external soft-start function. The soft-start function is used

to prevent large inrush current and output voltage overshoot

while the converter is being powered-up. The soft-start

function automatically begins once the chip is enabled.

There is a delay time around 1.1ms from EN goes high to

begins to ramp-up.

OUT

If the external capacitor between the SS pin and ground is

removed, the internal soft-start function will be chosen.

An internal current source charges the internal soft-start

capacitor so that the internal soft-start voltage ramps up

linearly. The output voltage will track the internal soft-start

voltage during the soft-start interval. After the internal soft-

start voltage exceeds the REFIN voltage, the output voltage

no longer tracks the internal soft-start voltage but follows

the REFIN voltage. Therefore, the duty cycle of the UGATE

signal as well as the input current at power up are limited.

The soft-start process is finished until both the single

internal SSOK and external SSOK go high and protection

is not triggered. Figure 8 shows the internal soft-start

sequence.

Enable and Disable

The EN pin is a high impedance input that allows power

sequencing between the controller bias voltage and another

voltage rail. The RT8813A remains in shutdown if the EN

pin is lower than 800mV. When the EN voltage rises above

the 1.6V high level threshold, the RT8813A will begin a

new initialization and soft-start cycle.

Power On Reset (POR), UVLO

Power On Reset (POR) occurs when V

rises above

PVCC

to approximately 4.1V (typical), the RT8813A will reset

the fault latch circuit and prepare for PWM operation. When

the V

is lower than 3.8V (typical), the Under Voltage

PVCC

Lockout (UVLO) circuitry inhibits switching by keeping

UGATE and LGATE low.

PVCC

OUT

Internal SS

External SS

Internal SSOK

External SSOK

LGATE

UGATE

PGOOD

Current Limit

Programming

Soft-Start

Normal

Discharged

Figure 8. Internal Soft-Start Sequence

Soft

DS8813A-05 December 2013www.richtek.com

RT8813A

The RT8813A also provides an external soft-start function,

and the external soft-start sequence is shown in Figure

9. The external capacitor connected from SS pin to GND

is charged by a 5μA current source to build a soft-start

voltage ramp. If the external soft-start function is chosen,

the external soft-start time should be set longer than

internal soft-start time to avoid output voltage tracking the

internal soft-start ramp. The recommended external soft-

start slew rate is from 0.1V/ms to 0.4V/ms.

PVCC

OUT

Internal SS

External SS

Internal SSOK

External SSOK

LGATE

UGATE

PGOOD

Current Limit

Programming

Soft-Start

Normal

Soft

Discharged

Figure 9. External Soft-Start Sequence

Power Good Output (PGOOD)

The PGOOD pin is an open drain output, and it requires a

pull-up resistor. During soft-start, the PGOOD is held low

and is allowed to be pulled high after V

achieved over

OUT

UVP threshold and under OVP threshold. In additional, if

any protection is triggered during operation, the PGOOD

will be pulled low immediately.

PWM VID and Dynamic Output Voltage Control

The RT8813A features a PWM VID input for dynamic output

voltage control as shown in Figure 11, which reduces the

number of device pin and enables a wide dynamic voltage

range. The output voltage is determined by the applied

voltage on the REFIN pin. The PWM duty cycle determines

the variable output voltage at REFIN.

VID

VREF

REFADJ

Buffer

RGND

REFIN

STANDBY

Standby

Mode Control

RGND

BOOT

REF2

PWM IN

REF1

RGND

REFADJ

Figure 11. PWM VID Analog Circuit Diagram

VCC

OUT

Figure 10. External Soft-Start Time Setting

The soft-start time can be calculated as :

(C V )



t =

Where ISS = 5μA (typ.), V

SS REFIN

is the voltage of REFIN

REFIN

With the external circuit and VID control signal, the

controller provides three operation modes shown as Figure

12.

VREF

REFIN

PWM VID

STANDBY

CONTROL

BOOT

MODE

NORMAL

MODE

BOOT

MODE

STANDBY

MODE

Figure 12. PWM VID Time Diagram

pin, and CSS is the external capacitor placed from SS to

GND.

DS8813A-05 December 2013 www.richtek.com

RT8813A

Boot Mode

VID is not driven, and the buffer output is tri-state. At this

time, turn off the switch Q1 and connect a resistor divider

as shown in Figure 11 that can set the REFIN voltage to

be V

V = V

BOOT VREF

Where V

Choose R

and R

REF1 BOOT

BOOT REF1

as the following equation :

BOOT







RRR

REF1 REF2 BOOT



= 2V (typ.)

VREF

to be approximately 10kΩ, and the R

REF2

can be calculated by the following equations :

BOOT

RVV



RVV

REF2 VREF BOOT



RVV

REF2 VREF BOOT



REF2 VREF BOOT





BOOT





BOOT

REF2



REF1





BOOT

Normal Mode

If the VID pin is driven by a PWM signal and switch Q1 is

disabled as shown in Figure 11, the V

from V

min

to V

PWM duty cycle and V

percent PWM duty cycle. The V

by the following equations :

V = V

min VREF

V = V



R R // (R R )

REF1 REFADJ BOOT REF2

max VREF

By choosing R

calculated by the following equation :

REFADJ



The relationship between VID duty and V

Standby Mode

An external control can provide a very low voltage to meet

operating in standby mode. If the VID pin is floating

OUT

and switch Q1 is enabled as shown in Figure 11, the REFIN

pin can be set for standby voltage according to the

calculation below :

V = V

STANDBY VREF

R// R

By choosing R



R R (R // R )

REF1 BOOT REF2 STANDBY

, R

REF1

REF2 STANDBY



REF2

, and R

BOOT

, the R

STANDBY

can

be calculated by the following equation :

STANDBY

RVV RRR

REF2 REF STANDBY REF1 REF2 BOOT



REF1



RRR V

 



REF2 REF1 BOOT STANDBY

   



Figure 13, and V

below :

V = V NV

OUT min STEP

where V

V =

where N

STEP

(V V )

is the number of total available voltage steps

max

and N is the number of step at a specific V

voltage VID period (T

unit pulse width (Tu) and the available step number (N

The recommended Tu is 27ns.

REFIN

N = 1

min

can be adjusted

REFIN

, where V

max



REF2 BOOT

R // (R R )

REFADJ BOOT REF2







(R // R ) R R

REF1 REFADJ BOOT REF2

, R

REF1



REF1 min



max min

can be set according to the calculation

OUT

is the voltage at zero percent

min

is the voltage at one hundred

max

and V

min

REF2

max



REF2



REF2

, and R

BOOT

, the R

REFIN

REFADJ

can be set

can be

is shown in

is the resolution of each voltage step 1.



max min

max

. The dynamic

OUT

N = 2

= Tu x N

vid

0.5

) is determined by the

max

N = N

max

VID Duty

max

N = 1

VID Input

N = 2

VID Input

= N

max

x T

vid

Figure 13. PWM VID Analog Output

DS8813A-05 December 2013www.richtek.com

RT8813A



VID Slew Rate Control

In RT8813A, the V

slew rate is proportional to PWM

REFIN

VID duty, the rising time and falling time is the same

because the voltage of REFIN pin traveling is the same. In

normal mode, the V

by C

When choose C

SR =

R = (R // R ) // (R +R )

SR REF1 REFADJ BOOT REF2

When choose C

SR =

R = R // R R // R

SR REF1 REFADJ BOOT REF2

or C

REFADJ

(V V ) 80%

REFIN_Final REFIN_initial

REFIN

REFADJ

2.2R C



REFIN

(V V ) 80%

REFIN_Final REFIN_initial

2.2R C







The recommend SR is estimated by C

slew rate SR can be estimated

REFIN

as the following equation :



SR REFADJ



SR REFIN



REFADJ

Current limit

The RT8813A provides cycle-by-cycle current limit control

by detecting the PHASE voltage drop across the low side

MOSFET when it is turned on. The current limit circuit

employs a unique “valley” current sensing algorithm as

shown in Figure 14. If the magnitude of the current sense

signal at PHASE is above the current limit threshold, the

PWM is not allowed to initiate a new cycle.

L,PEAK

LOAD

L,VALLEY

Figure 14. “Valley” Current Limit

In order to provide both good accuracy and a cost effective

solution, the RT8813A supports temperature compensated

MOSFET R

DS(ON)

sensing.

In an over current condition, the current to the load exceeds

the average output inductor current. Thus, the output

voltage falls and eventually crosses the under voltage

protection threshold, inducing IC shutdown.

Current Limit Setting

Current limit threshold can be set by a resistor (R

OCSET

between LGATE1 and GND. Once PVCC exceeds the

POR threshold and chip is enabled, an internal current

source I

OCSET

flows through R

OCSET

. The voltage across

OCSET

is stored as the current limit protection threshold

. The threshold range of V

is 50mV to 400mV.

OCSET

After that, the current source is switched off.

R =

where I

(valley inductor current) and I

can be determined using the following equation :

OCSET

IR 40mV



VALLEY LGDS(ON)

represents the desired inductor limit current

VALLEY



OCSET

is current limit setting

OCSET

current which has a temperature coefficient to compensate

the temperature dependency of the R

If R

is not present, there is no current path for I

OCSET

DS(ON)

OCSET

to build the current limit threshold. In this situation, the

current limit threshold is internally preset to 400mV

(typical).

Negative Current Limit

The RT8813A supports cycle-by-cycle negative current

limiting. The absolute value of negative current limiting

threshold is the same with the positive current limit

threshold. If negative inductor current is rising to trigger

negative current limit, the low side MOSFET will be turned

off and the current will flow to input side through the body

diode of the high side MOSFET. At this time, output voltage

tends to rise because this protection limits current to

discharge the output capacitor. In order to prevent shutdown

because of over voltage protection, the low side MOSFET

is turned on again 400ns after it is turned off. If the device

hits the negative over current threshold again before output

voltage is discharged to the target level, the low side

MOSFET is turned off and process repeats. It ensures

maximum allowable discharge capability when output

voltage continues to rise. On the other hand, if the output

is discharged to the target level before negative current

threshold is reached, the low side MOSFET is turned off,

the high side MOSFET is then turned on, and the device

keeps normal operation.

)

DS8813A-05 December 2013 www.richtek.com

RT8813A



Current Balance

The RT8813A implements current balance mechanism in

the current loop. The RT8813A senses per phase current

signal and compares it with the average current. If the

sensed current of any particular phase is higher than the

average current, the on-time of this phase will be

decreased.

The current balance accuracy is major related with on-

resistance of low side MOSFET (R

practical application, using lower R

LG,DS(ON)

). That is, in

will reduce

the current balance accuracy.

Output Over Voltage Protection (OVP)

The output voltage can be continuously monitored for over

voltage protection. If REFIN voltage is lower than 1.33V,

the over voltage threshold follows to absolute over voltage

2V. If REFIN voltage is higher than 1.33V, the over voltage

threshold follows relative over voltage 1.5 x V

REFIN

. When

OVP is triggered, UGATE goes low and LGATE is forced

high. The RT8813A is latched once OVP is triggered and

can only be released by PVCC or EN power on reset. A

5μs delay is used in OVP detection circuit to prevent false

trigger.

Output Under Voltage Protection (UVP)

The output voltage can be continuously monitored for under

voltage protection. When the output voltage is less than

40% of its set voltage, under voltage protection is triggered

and then all UGATEx and LGATEx gate drivers are forced

low. There is a 3μs delay built in the UVP circuit to prevent

false transitions. During soft-start, the UVP blanking time

is equal to PGOOD blanking time.

Thermal Monitoring and Temperature Reporting

The RT8813A provides thermal monitoring function in 2/1

phase operation via sensing the TSNS pin voltage, and

which can indicate ambient temperature through the voltage

divider R

of V

TSNS

temperature rises, V

OTSET

and R

shown in Figure 15. The voltage

NTC

is typically set to be higher than 1V. When ambient

will fall and the TALERT signal

TSNS

will be pulled to low level if TSNS voltage drops below 1V.

TSNS

OTSET

TSNS

NTC

Internal OTP

CMP

TALERT

Figure 15. External OTP Setting

where R

can be determined using the following equation :

OTSET

R = R V1

OTSET NTC,T C X

NTC,T°C



is the thermistor's resistance at OTP trigger





temperature.

The standard formula for the resistance of the NTC

thermistor as a function of temperature is given by :













R = Re

where R



NTC,T C 25 C

is the thermistor's nominal resistance at room

25°C









T 273 298

temperature 25°C, β (beta) is the thermistor's material

constant in Kelvins, and T is the thermistor's actual

temperature in Celsius.

MOSFET Gate Driver

The RT8813A integrates high current gate drivers for the

MOSFETs to obtain high efficiency power conversion in

synchronous Buck topology. A dead-time is used to prevent

the crossover conduction for high side and low side

MOSFETs. Because both the two gate signals are off

during the dead-time, the inductor current freewheels

through the body diode of the low side MOSFET. The

freewheeling current and the forward voltage of the body

diode contribute power losses to the converter. The

RT8813A employs adaptive dead-time control scheme to

ensure safe operation without sacrificing efficiency.

Furthermore, elaborate logic circuit is implemented to

prevent cross conduction. For high output current

applications, two power MOSFETs are usually paralleled

to reduce R

. The gate driver needs to provide more

DS(ON)

current to switch on/off these paralleled MOSFETs. Gate

driver with lower source/sink current capability results in

longer rising/falling time in gate signals and higher

switching loss. The RT8813A embeds high current gate

drivers to obtain high efficiency power conversion.

DS8813A-05 December 2013www.richtek.com

RT8813A

Inductor Selection

Inductor plays an importance role in step-down converters

because the energy from the input power rail is stored in

it and then released to the load. From the viewpoint of

efficiency, the DC Resistance (DCR) of inductor should

be as small as possible to minimize the copper loss. In

additional, the inductor occupies most of the board space

so the size of it is important. Low profile inductors can

save board space especially when the height is limited.

However, low DCR and low profile inductors are usually

not cost effective.

Additionally, higher inductance results in lower ripple

current, which means the lower power loss. However, the

inductor current rising time increases with inductance value.

This means the transient response will be slower. Therefore,

the inductor design is a trade-off between performance,

size and cost.

In general, inductance is designed to let the ripple current

ranges between 20% to 40% of full load current. The

inductance can be calculated using the following equation :

VV V



L =

min

IN OUT OUT

FkI V



SW OUT_rated IN



where k is the ratio between inductor ripple current and

rated output current.

Input Capacitor Selection

Voltage rating and current rating are the key parameters

in selecting input capacitor. Generally, input capacitor has

a voltage rating 1.5 times greater than the maximum input

voltage is a conservatively safe design.

The input capacitor is used to supply the input RMS

current, which can be approximately calculated using the

following equation :

I = I 1

RMS OUT





OUT OUT



IN IN



Output Capacitor Selection

The output filter capacitor must have ESR low enough to

meet output ripple and load transient requirement, yet have

high enough ESR to satisfy stability requirements. Also,

the capacitance must be high enough to absorb the inductor

energy going from a full load to no load condition without

tripping the OVP circuit. Organic semiconductor

capacitor(s) or special polymer capacitor(s) are

recommended.

MOSFET Selection

The majority of power loss in the step-down power

conversion is due to the loss in the power MOSFETs. For

low voltage high current applications, the duty cycle of

the high side MOSFET is small. Therefore, the switching

loss of the high side MOSFET is of concern. Power

MOSFETs with lower total gate charge are preferred in

such kind of application.

However, the small duty cycle means the low side MOSFET

is on for most of the switching cycle. Therefore, the

conduction loss tends to dominate the total power loss of

the converter. To improve the overall efficiency, the

MOSFETs with low R

are preferred in the circuit

DS(ON)

design. In some cases, more than one MOSFET are

connected in parallel to further decrease the on-state

resistance. However, this depends on the low side

MOSFET driver capability and the budget.

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 :

The next step is to select proper capacitor for RMS current

rating. Use more than one capacitor with low Equivalent

Series Resistance (ESR) in parallel to form a capacitor

bank is a good design. Besides, placing ceramic capacitor

where T

D(MAX)

= (T

J(MAX)

− TA) / θ

J(MAX)

is the maximum junction temperature, TA is

the ambient temperature, and θ

thermal resistance.

is the junction to ambient

close to the drain of the high side MOSFET is helpful in

reducing the input voltage ripple at heavy load.

DS8813A-05 December 2013 www.richtek.com

RT8813A

For recommended operating condition specifications, the

maximum junction temperature is 125°C. The junction to

ambient thermal resistance, θJA, is layout dependent. For

WQFN-24L 4x4 package, the thermal resistance, θJA, is

28°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 :

= (125°C − 25°C) / (28°C/W) = 3.57W for

D(MAX)

WQFN-24L 4x4 package

The maximum power dissipation depends on the operating

ambient temperature for fixed T

and thermal

J(MAX)

resistance, θJA. The derating curve in Figure 16 allows

the designer to see the effect of rising ambient temperature

on the maximum power dissipation.

4.0

3.5

3.0

2.5

2.0

1.5

Four-Layer PCB

Layout Considerations

Layout is very important in high frequency switching

converter design. If designed improperly, the PCB could

radiate excessive noise and contribute to the converter

instability. Following layout guidelines must be considered

before starting a layout for RT8813A.

 Place the RC filter as close as possible to the PVCC

pin.

 Keep current limit setting network as close as possible

to the IC. Routing of the network should avoid coupling

to high voltage switching node.

 Connections from the drivers to the respective gate of

the high side or the low side MOSFET should be as

short as possible to reduce stray inductance.

 All sensitive analog traces and components such as

VSNS, RGND, EN, PSI, VID, PGOOD, VREF, TON

VREFADJ, VREFIN and TSNS should be placed away

from high voltage switching nodes such as PHASE,

LGATE, UGATE, or BOOT nodes to avoid coupling. Use

internal layer(s) as ground plane(s) and shield the

feedback trace from power traces and components.

1.0

0.5

Maximum Power Dissipation (W) 1

0.0 0 25 50 75 100 125

Ambient Temperature (°C)

Figure 16. Derating Curve of Maximum Power

Dissipation

 Power sections should connect directly to ground

plane(s) using multiple vias as required for current

handling (including the chip power ground connections).

Power components should be placed to minimize loops

and reduce losses.

DS8813A-05 December 2013www.richtek.com

Outline Dimension

RT8813A

SEE DETAIL A

1 2

DETAIL A

Pin #1 ID and Tie Bar Mark Options

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

1 2

but must be located within the zone indicated.

Dimensions In Millimeters 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 0.180 0.300 0.007 0.012

D 3.950 4.050 0.156 0.159

Option 1 2.400 2.500 0.094 0.098

Option 2 2.650 2.750 0.104 0.108

E 3.950 4.050 0.156 0.159

Option 1 2.400 2.500 0.094 0.098

Option 2 2.650 2.750 0.104 0.108

e 0.500 0.020

L 0.350 0.450 0.014 0.018

Richtek Technology Corporation

14F, No. 8, Tai Yuen 1st Street, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789

W-Type 24L QFN 4x4 Package

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.

DS8813A-05 December 2013 www.richtek.com

Richtek RT8813AGQW Schematic [ru]

Specifications and Main Features

Frequently Asked Questions

User Manual