Richtek RT8811AGQW Schematic [ru]

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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 RDS(ON) current sensing technique. Current limit is accomplished through continuous inductor- current-sense, while RDS(ON) current sensing is used for accurate channel current balance. Using the method of current sampling utilizes the best advantages of each technique.

The RT8811A features external reference input and PWMVID 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.

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 RDS(ON) Current Sensing for Current Balance

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

Simplified Application Circuit

VPVCC

VIN

PGOOD

 

RT8811A

VIN

PVCC

 

BOOT1

 

 

 

UGATE1

 

TON

 

PHASE1

VOUT

 

LGATE1

 

PGOOD

 

VIN

 

 

 

 

 

BOOT2

 

PSI

 

UGATE2

 

 

 

 

VID

 

PHASE2

 

EN

 

LGATE2

 

 

 

 

 

GND

RGND

VGND_SNS

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8811A-02 March 2014

www.richtek.com

 

1

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

Marking Information

 

0T= : Product Code

0T=YM

YMDNN : Date Code

DNN

 

 

 

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 requirements of IPC/JEDEC J-STD-020.

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

Pin Configurations

(TOP VIEW)

PHASE1 LGATE1 GND PVCC LGATE2 PHASE2

 

24

23

22

21

20

19

 

BOOT1 1

 

 

 

 

18

BOOT2

UGATE1 2

 

 

 

 

17

UGATE2

EN 3

 

GND

 

16

PGOOD

PSI 4

 

 

15

VCC

 

 

 

 

VID 5

 

 

 

25

14

TALERT

REFADJ 6

 

 

 

 

13

TSNS

7

8

9

10

11

12

 

REFIN

VREF

TON

RGND

VSNS

SS

 

WQFN-24L 4x4

 

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

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,

3

EN

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

4

PSI

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.

5

VID

Programming Output

Voltage Control Input. Refer to PWM-VID Dynamic

Voltage Control.

 

 

 

 

6

REFADJ

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

 

 

 

7

REFIN

External Reference Input.

 

 

 

8

VREF

Reference Voltage Output. This is a high precision voltage reference (2V)

from the VREF pin to the RGND pin.

 

 

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

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

output load.

 

 

 

 

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS8811A-02 March 2014

2

 

 

 

 

 

RT8811A

 

 

 

 

 

Pin No.

 

Pin Name

Pin Function

 

 

 

 

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

12

 

SS

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

 

 

 

 

will be chose.

13

 

TSNS

Temperature Sensing Input.

 

 

 

 

 

14

 

 

Thermal Alert. Active low open-drain output.

 

TALERT

 

15

 

VCC

LDO Regulator Output. Connect a minimum 4.7 F ceramic capacitor between

 

this pin and ground.

 

 

 

 

16

 

PGOOD

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

 

 

 

 

 

17

 

UGATE2

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.

 

 

 

 

18

 

BOOT2

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

 

 

 

 

 

19

 

PHASE2

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.

 

 

 

 

20

 

LGATE2

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.

 

 

 

 

21

 

PVCC

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

 

GND.

 

 

 

 

22,

 

 

 

Ground. Must be connected to GND on PCB. The Exposed pad should be

 

GND

soldered to a large PCB and connected to GND for maximum thermal

25 (Exposed Pad)

 

 

 

 

 

dissipation.

23

 

LGATE1

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.

 

 

 

 

 

 

 

 

 

24

 

PHASE1

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.

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8811A-02 March 2014

www.richtek.com

 

3

Richtek RT8811AGQW Schematic

RT8811A

Function Block Diagram

 

 

VREF

RGND

VCC

 

 

 

 

 

 

 

Reference Output

Internal

 

PVCC

VID

 

 

Gen. & BG

Regulator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

REFADJ

 

RGND

 

 

Power On Reset VCC

VA

 

 

 

 

Mode Select

 

 

 

PSI

 

OV

 

& Central Logic

 

 

 

 

 

 

 

 

 

 

 

PGOOD

REFIN

150% REFIN

+

 

 

 

 

 

 

 

 

 

 

 

 

 

UV

-

Control & Protection Logic

 

 

 

 

 

40% REFIN

+

 

 

 

 

 

 

 

 

Soft-Start

-

 

 

Boot-Phase

 

 

 

 

PWM

 

 

 

 

 

 

 

 

Detection 1

 

 

 

& Slew Rate

CMP

 

 

 

 

 

 

 

 

Control

+

 

 

Boot-Phase

 

 

VSNS

 

 

-

 

 

 

 

VA

 

 

 

Detection 2

 

 

 

 

 

 

 

 

 

 

BOOT1

 

2µA

 

 

TON

 

 

 

 

 

 

 

 

 

UGATE1

 

 

 

Gen 1

 

 

 

 

 

 

 

 

 

 

 

PHASE1

 

 

Enable

To Driver Logic

 

 

PWM1

 

 

EN

 

 

 

 

 

LGATE1

 

Logic

To Power On Reset

 

 

 

 

 

 

 

 

 

 

Driver

 

 

 

 

 

 

 

 

 

 

 

 

VIN

 

 

TON

PWM2

Logic

 

BOOT2

TON

 

To Power On Reset

 

 

 

UGATE2

 

 

Detection

 

 

Gen 2

 

 

 

PHASE2

 

 

 

 

 

 

 

 

 

TALERT

 

 

 

 

 

 

 

 

LGATE2

 

 

 

 

 

 

 

 

 

TSNS

1V

+

 

 

 

 

 

 

 

 

-

 

 

 

 

S/H

+

 

 

 

 

 

 

 

 

VB

 

Internal

 

 

Current

 

 

-

 

Die Temperature

 

 

Balance

 

S/H

+

 

 

 

 

 

 

 

 

 

Sense

 

 

 

 

-

VB

 

 

 

 

 

Current

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Limit

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS8811A-02 March 2014

4

 

RT8811A

Operation

The RT8811Aintegrates 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 TONGenx, 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

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.

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 overvoltage protection. When the output voltage exceeds its set voltage threshold (If VREFIN 1.33V, OV = 2V, or VREFIN > 1.33V, OV = 1.5 x VREFIN), UGATE goes low and LGATE is forced high. The controller is latched until VCC is resupplied and exceeds the POR rising threshold voltage.

Under-Voltage Protection (UVP)

The output voltage is continuously monitored for undervoltage 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.

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8811A-02 March 2014

www.richtek.com

 

5

RT8811A

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

 

TONtoGND -------------------------------------------------------------------------------------------------------

 

 

 

 

−0.3 to 32V

 

PVCC to GND ----------------------------------------------------------------------------------------------------

 

 

 

 

−0.3 to 15V

 

RGNDtoGND ----------------------------------------------------------------------------------------------------

 

 

 

 

−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 (VBOOT + 0.3V)

<20ns --------------------------------------------------------------------------------------------------------------

 

 

 

 

−5V to (VBOOT + 5V)

LGATEx to GND

 

 

 

 

 

 

 

 

 

DC -------------------------------------------------------------------------------------------------------------------

 

 

 

 

−0.3V to (VPVCC + 0.3V)

<20ns --------------------------------------------------------------------------------------------------------------

 

 

 

 

−5V to (VPVCC + 5V)

Other Pins---------------------------------------------------------------------------------------------------------

 

 

 

 

−0.3V to 6V

 

Power Dissipation, PD @ TA = 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

 

 

 

Recommended Operating Conditions

(Note 4)

 

 

 

 

 

 

Supply Input Voltage, VIN --------------------------------------------------------------------------------------

 

 

 

 

7V to 20V

 

Control Voltage, VPVCC -----------------------------------------------------------------------------------------

 

 

 

 

4.5V to 13.2V

 

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

 

 

 

 

−40°C to 125°C

 

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

 

 

 

 

−40°C to 85°C

 

Electrical Characteristics

 

 

 

 

 

 

 

 

(TA = 25°C unless otherwise specified)

 

 

 

 

 

 

 

 

Parameter

Symbol

Test Conditions

Min

Typ

 

Max

 

Unit

PWM Controller

 

 

 

 

 

 

 

 

 

PVCC Supply Voltage

VPVCC

 

 

4.5

--

 

13.2

 

V

PVCC Supply Current

ISUPPLY

EN = 3.3V, Not Switching

--

2

 

4

 

mA

PVCC Shutdown Current

ISHDN

EN = 0V, VCC Remains Active

--

--

 

220

 

A

VCC POR Threshold

 

 

 

3.7

4

 

4.3

 

V

 

 

 

 

 

 

 

 

 

 

POR Hysteresis

 

 

 

--

0.3

 

--

 

V

VCC (LDO Output)

 

PVCC > 10.8V; IVCC < 220mA

4.75

5

 

5.25

 

V

 

 

 

 

 

 

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS8811A-02 March 2014

6

 

RT8811A

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

VCC Output Current

 

VCC = 4.5V

220

--

400

mA

Switching Frequency

 

RTON = 500k (Note 5)

270

300

330

kHz

Minimum TON

 

TON(MIN)

 

--

70

--

ns

Minimum Off-Time

 

TOFF(MIN)

 

--

300

--

ns

Zero Current Crossing

 

 

8

--

8

mV

Threshold

 

 

 

 

 

 

 

 

 

 

EN Threshold

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EN Input Voltage

 

Logic-High

VENH

 

1.6

--

--

V

 

Logic-Low

VENL

 

--

--

0.8

 

 

 

 

Mode Decision

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PSI High Threshold

VPSIH

Enable Two Phases with FCCM

2.4

--

--

V

 

 

 

 

 

 

 

 

PSI Low Threshold

 

VPSIL

Enable One Phase with DEM

--

--

0.8

V

VID Input Voltage

 

Logic-High

VVIDH

 

2

--

--

V

 

Logic-Low

VVIDL

 

--

--

1

 

 

 

 

Protection Function

 

 

 

 

 

 

Current Limit Setting Current

IOCSET

 

9

10

11

A

 

 

 

 

 

 

 

Current Limit Setting Current

IOCSET_TC

On the basis of 25 C

--

6300

--

ppm/ C

Temperature Coefficient

Current Limit Threshold

 

 

20

--

20

mV

 

 

 

 

 

 

 

Current Limit Threshold

 

 

50

--

300

mV

Setting Range

 

 

 

 

 

 

 

 

 

 

Absolute Over-Voltage

VOVP, Absolute

VREFIN 1.33V

1.9

2

2.1

V

Protection Threshold

 

 

 

 

 

 

Relative Over-Voltage

VOVP, Relative

VREFIN > 1.33V

145

150

155

%

Protection Threshold

 

 

 

 

 

 

OVP Delay

 

tD_OVP

 

--

5

--

s

Relative Under-Voltage

VUVP

UVP

35

40

45

%

Protection Threshold

UVP Delay

 

tD_UVP

 

--

3

--

s

Internal Die Temperature

 

 

--

95

--

C

Sense Threshold

 

 

 

 

 

 

 

 

 

 

Thermal Shutdown Threshold

TSD

 

--

140

--

C

TSNS Threshold

 

VTSEN

(No Shutting Down)

0.98

1

1.02

V

PGOOD Blanking Time

 

From EN = High to PGOOD = High with

--

3.7

--

ms

 

VOUT within Regulation Point

 

 

 

 

 

 

 

 

VOUT Internal Soft-Start Time

TSS

From First UGATE to VOUT Regulation

--

0.7

--

ms

Point, VREFIN = 1V and VOUT Initial = 0V

 

 

 

 

 

 

 

 

Soft-Start Current Source

ISS

 

--

5

--

A

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8811A-02 March 2014

www.richtek.com

 

7

RT8811A

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

 

 

 

 

 

 

 

Error Amplifier

 

 

 

 

 

 

VSNS Error Comparator

 

VREFIN = 1V

5

--

5

mV

Threshold (Valley)

 

Reference

 

 

 

 

 

 

 

 

 

 

 

 

 

Reference Voltage

VVREF

Sourcing Current = 1mA, VID No

1.98

2

2.02

V

Switching

Driver On-Resistance

 

 

 

 

 

 

 

 

 

 

 

 

 

UGATE Driver Source

RUGATEsr

IUGATEx = 150mA

--

1.5

3

 

UGATE Driver Sink

RUGATEsk

VUGATEx VPHASEx = 0.1V

--

2

4

 

LGATE Driver Source

RLGATEsr

ILGATEx = 150mA

--

1.5

3

 

LGATE Driver Sink

RLGATEsk

VLGATEx = 0.1V

--

0.7

1.4

 

Dead-Time

 

From LGATE falling to UGATE rising

--

30

--

ns

 

 

 

 

 

 

From UGATE falling to LGATE rising

--

30

--

 

 

 

 

 

 

 

 

 

 

Boost Switch Ron

RBOOT

PVCC to BOOTx, IBOOT = 10mA

--

40

80

 

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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package.

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

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

Note 5. Not production tested. Test condition is VIN = 8V, VOUT = 1V, IOUT = 20A using application circuit.

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS8811A-02 March 2014

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