Richtek RT8811AGQW Schematic [ru]

RT8811A

Dual-Phase COT Buck PWM Controller with Dynamic Voltage Control

General Description

The RT8811A is a dual-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 RT8811A 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 RT8811A 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



 Dual-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



 Built-In 220mA 5V LDO



 Adjustable Current Limit Threshold



 Adjustable Switching Frequency



 UVP/OVP Protection



 Shoot-Through Protection and Short Pulse Free



Technology



 Single IC Supply Voltage : 4.5V to 13.2V



 Support an Ultra-Low Output Voltage as Standby



Voltage



 Thermal Shutdown



 Thermal Alert Indicator



 Power Good Indicator



 RoHS Compliant and Halogen Free



Current Sensing for Current Balance

DS(ON)

Simplified Application Circuit

RT8811A

PVCC

BOOT1

UGATE1

PHASE1

PGOOD

TON

PGOOD

PSI

VID

GND

UGATE2

PHASE2

RGND

DS8811A-02 March 2014 www.richtek.com

OUT

GND_SNS

RT8811A

Applications

 Motherboard to High End GPU Core Power

 High End Desktop PC Memory Core Power

 Low Voltage. High Current DC/DC Converter

 Voltage Regulator Modules

Ordering Information

RT8811A

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.

Marking Information

0T= : Product Code

0T=YM

YMDNN : Date Code

DNN

Pin Configurations

(TOP VIEW)

LGATE1

GND

VREF

GND

21 20 1924 2223

TON

PVCC

RGND

BOOT1

UGATE1

EN PSI VID

REFADJ

PHASE1

78910 1211

REFIN

WQFN-24L 4x4

PHASE2

LGATE2

BOOT2

UGATE2

PGOOD

VCC

TALERT

TSNS

VSNS

Function Pin Description

Pin No. Pin Name Pin Function

1 BOOT1 Bootstrap Supply for PWM 1. This pin powers the high-side MOSFET driver.

High-Side Driver of PWM 1. This pin provides the gate drive for the

2 UGATE1

3 EN

4 PSI

5 VID

6 REFADJ Reference Adjustment Output. Refer to PWM-VID Dynamic Voltage Control.

7 REFIN External Reference Input.

8 VREF

9 TON ON-Time/Switching Frequency Adjustment Input.

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

11 VSNS

converter's high-side MOSFET. Connect this pin to the Gate of high-side MOSFET.

Enable Control Input. Drive EN higher than 1.6V to turn on the controller, lower than 0.8V to turn it off. If the EN pin is open, it will be pulled to high by internal circuit.

Power Saving Interface. When the voltage is pulled below 0.8V, the device will operate into 1 phase DEM. When the voltage is between 2.4V to 5.5V, the device will operate into 2 phases force CCM.

Programming Output Voltage Control Input. Refer to PWM-VID Dynamic Voltage Control.

Reference Voltage Output. This is a high precision voltage reference (2V) from the VREF pin to the RGND pin.

Positive Remote Sense Input. Connect this pin to the positive terminal of output load.

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Pin No. Pin Name Pin Function

Soft-Start Time Setting. Connect an external capacitor to adjust soft-start

12 SS

13 TSNS Temperature Sensing Input.

time. When the external capacitor is removed, the internal soft-start function will be chose.

RT8811A

15 VCC

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

17 UGATE2

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

19 PHASE2

20 LGATE2

21 PVCC

22,

25 (Exposed Pad)

23 LGATE1

24 PHASE1

TALERT

GND

Thermal Alert. Active low open-drain output. LDO Regulator Output. Connect a minimum 4.7F ceramic capacitor between

this pin and ground.

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

Switch Node for PWM2. Connect this pin to the Source of high-side MOSFET together with the Drain of low-side MOSFET and the inductor.

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

Supply Voltage Input. Place a high quality bypass capacitor from this pin to GND.

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

Low-Side 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 MOSFET.

Switch Node for PWM1. Connect this pin to the Source of high-side MOSFET together with the Drain of low-side MOSFET and the inductor.

DS8811A-02 March 2014 www.richtek.com

RT8811A

Function Block Diagram

VID

REFADJ

PSI

REFIN

VSNS

TON

TALERT

TSNS

VREF

RGND

150% REFIN

40% REFIN

Soft-Start

& Slew Rate

Control

2µA

Enable

Logic

VIN

Detection

Internal

Die Temperature

Sense

RGND

Reference Output

Gen. & BG

Mode Select

PWM

CMP

To Driver Logic To Power On Reset

To Power On Reset

Power On Reset

& Central Logic

Control & Protection Logic

TON

Gen 1

TON

Gen 2

VCC

Current

Balance

Current

Limit

VCC

Internal

Regulator

Boot-Phase Detection 1

Boot-Phase Detection 2

PWM1

Driver

Logic

PWM2

S/H

PVCC

PGOOD

BOOT1 UGATE1 PHASE1

LGATE1

BOOT2 UGATE2

PHASE2

LGATE2

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Operation

RT8811A

The RT8811A integrates a Constant-On-Time (COT) PWM

controller, the controller provides the PWM signal which

relies on the output ripple voltage comparing with internal

reference voltage. 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.

The RT8811A 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.

Current Balance

The RT8811A implements the internal current balance

mechanism in the current loop. The RT8811A 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.

PGOOD

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)

The output voltage can be continuously monitored for over-

voltage protection. When the output voltage exceeds its

set voltage threshold (If V

> 1.33V, OV = 1.5 x V

REFIN

≤ 1.33V, OV = 2V, or V

REFIN

), UGATE goes low and LGATE

is forced high. The controller is latched until VCC is re-

supplied and exceeds the POR rising threshold voltage.

Under-Voltage Protection (UVP)

The output voltage is 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 both UGATE and LGATE gate drivers are forced

low. The controller is latched until VCC is re-supplied and

exceeds the POR rising threshold voltage.

The power good output is an open-drain architecture.

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

output will be high impedance.

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 GND will be charged by a current

source and determines the soft-start time.

DS8811A-02 March 2014 www.richtek.com

RT8811A

Absolute Maximum Ratings (Note 1)

 TON to GND ------------------------------------------------------------------------------------------------------- −0.3 to 32V

 PVCC to GND ---------------------------------------------------------------------------------------------------- −0.3 to 15V

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

 PHASEx to GND

DC------------------------------------------------------------------------------------------------------------------- −0.3V to 26V

<20ns -------------------------------------------------------------------------------------------------------------- −8V to 38V

 BOOTx to PHASEx --------------------------------------------------------------------------------------------- 15V

 UGATEx to GND

DC------------------------------------------------------------------------------------------------------------------- 0.3V to (V

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

 LGATEx to GND

DC------------------------------------------------------------------------------------------------------------------- −0.3V to (V

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

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

 Power Dissipation, P

@ T

= 25°C

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

BOOT

PVCC

+ 0.3V)

+ 5V)

+ 0.3V)

+ 5V)

Recommended Operating Conditions (Note 4)

 Supply Input Voltage, V

 Control Voltage, V

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

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

PVCC

-------------------------------------------------------------------------------------- 7V to 20V

----------------------------------------------------------------------------------------- 4.5V to 13.2V

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

VCC POR Threshold 3.7 4 4.3 V

POR Hysteresis -- 0.3 -- V

VCC (LDO Output) PVCC > 10.8V; I

4.5 -- 13.2 V

PVCC

SUPPLY

SHDN

EN = 3.3V, Not Switching -- 2 4 mA

EN = 0V, VCC Remains Active -- -- 220 A

< 220mA 4.75 5 5.25 V

VCC

DS8811A-02 March 2014www.richtek.com

RT8811A

Parameter Symbol Test Conditions Min Typ Max Unit

VCC Output Current VCC = 4.5V 220 -- 400 mA

Switching Frequency R

Minimum TON T

Minimum Off-Time T

Zero Current Crossing Threshold

ON(MIN)

OFF(MIN)

8 -- 8 mV

-- 70 -- ns

-- 300 -- ns

= 500k (Note 5) 270 300 330 kHz

TON

EN Threshold

EN Input Voltage

Logic-High V

Logic-Low V

1.6 -- --

ENH

-- -- 0.8

ENL

Mode Decision

PSI High Threshold V

PSI Low Threshold V

Logic-High V

VID Input Voltage

Logic-Low V

Enable Two Phases with FCCM 2.4 -- -- V

PSIH

Enable One Phase with DEM -- -- 0.8 V

PSIL

2 -- --

VIDH

-- -- 1

VIDL

Protection Function

Current Limit Setting Current I

Current Limit Setting Current Temperature Coefficient

9 10 11 A

OCSET

OCSET_TC

On the basis of 25C -- 6300 -- ppm/C

Current Limit Threshold 20 -- 20 mV

Current Limit Threshold Setting Range

Absolute Over-V oltage Protection Threshold

Relative Over-Voltage Protection Threshold

OVP Delay

Relative Under-Voltage Protection Threshold

UVP Delay

Internal Die Temperature Sense Threshold

50 -- 300 mV

OVP, Absolute VREFIN

OVP, Relative VREFIN

D_OVP

UVP 35 40 45 %

UVP

D_UVP

-- 5 -- s

-- 3 -- s

-- 95 -- C

 1.33V 1.9 2 2.1 V

> 1.33V 145 150 155 %

Thermal Shutdown Threshold TSD -- 140 -- C

TSNS Threshold V

PGOOD Blanking Time

Internal Soft-Start Time TSS

OUT

(No Shutting Down) 0.98 1 1.02 V

TSEN

From EN = High to PGOOD = High with

within Regulation Point

OUT

From First UGATE to V Point, V

REFIN

= 1V and V

Regulation

OUT

Initial = 0V

-- 3.7 -- ms

-- 0.7 -- ms

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

DS8811A-02 March 2014 www.richtek.com

RT8811A

Parameter Symbol Test Conditions Min Typ Max Unit

Er ror Am p l if ier

VSNS Error Comparator Threshold (Valley)

Reference

= 1V 5 -- 5 mV

REFIN

Reference Voltage V

VREF

Sourcing Current = 1mA, VID No Switching

1.98 2 2.02 V

Driver On-Resistance

UGATE Driver Source R

UGATE Driver Sink R

LGATE Driver Source R

LGATE Driver Sink R

UGATEsr

UGATEsk

LGATEsr

LGATEsk

Dead-Time

UGATEx

LGATEx

= 150mA -- 1.5 3 

UGATEx

 V

PHASEx

= 0.1V -- 2 4 

= 150mA -- 1.5 3 

= 0. 1V -- 0.7 1.4 

LGATEx

From LGATE falling to UGATE rising -- 30 --

From UGATE falling to LGATE rising -- 30 --

Boost Switch Ron R

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.

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

PVCC to BOOTx, I

BOOT

= 8V, V

OUT

= 1V, I

= 10mA -- 40 80 

BOOT

= 20A using application circuit.

OUT

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