Richtek RT8812AGQW Schematic [ru]

Loading...

®

RT8812A

Dual-Phase PWM Controller with PWM-VID Reference

General Description

The RT8812A is a 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-20L 3x3 package.

The RT8812A 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 RT8812A 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

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 Shutdown

Power Good Indicator

RoHS Compliant and Halogen Free

Applications

CPU/GPU Core Power Supply

Notebook PC Memory Power Supply

Chipset/RAM Power Supply

Generic DC/DC Power Regulator

Simplified Application Circuit

VPVCC

PVCC

RT8812A

VIN

BOOT1

 

 

UGATE1

 

 

TON

PHASE1

VOUT

VIN

LGATE1

 

 

PGOOD

VIN

 

 

BOOT2

 

 

 

 

PSI

UGATE2

 

 

 

 

 

VID

PHASE2

 

 

LGATE2

 

 

EN

RGND

VGND_SNS

 

GND

 

VSNS

VOUT_SNS

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8812A-04 November 2013

www.richtek.com

 

1

RT8812A

Ordering Information

Pin Configurations

RT8812A

(TOP VIEW)

 

Package Type

 

PHASE1

LGATE1

PVCC

LGATE2

PHASE2

 

 

Lead Plating System

 

 

 

QW : WQFN-20L 3x3 (W-Type)

 

 

 

 

 

 

 

 

G : Green (Halogen Free and Pb Free)

BOOT1

20 19 18 17 16

BOOT2

Note :

 

1

 

 

 

15

 

UGATE1

2

 

 

 

14

UGATE2

Richtek products are :

GND

EN

3

13

PGOOD

RoHS compliant and compatible with the current require-

PSI

4

 

 

21

12

VSNS

VID

5

 

 

 

11

SS

ments of IPC/JEDEC J-STD-020.

 

 

 

 

6

7

8

9

10

 

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

 

REFADJ

REFIN

VREF

TON

RGND

 

Marking Information

 

 

 

WQFN-20L 3x3

 

 

0Z= : Product Code

 

 

 

 

 

 

 

0Z=YM

YMDNN : Date Code

 

 

 

 

 

 

 

DNN

 

 

 

 

 

 

 

 

Function Pin Description

Pin No.

Pin Name

 

Pin Function

 

1

BOOT1

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

 

2

UGATE1

High Side Gate Driver of PWM 1. This pin provides the gate drive for the converter's

 

high side MOSFET. Connect this pin to the Gate of high side MOSFET.

 

 

 

 

 

 

 

 

3

EN

Enable Control Input. Active high 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 between 1.2V to 1.8V, the device will operate

 

into 1 phase force CCM. When the voltage is between 2.4V to 5.5V, the device will

 

 

 

 

 

 

operate into 2 phase 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 RGND pin.

 

 

 

 

 

 

9

TON

ON-Time/Switching Frequency Adjustment Input. Connect a 100pF ceramic capacitor

 

between CTON and ground is optional for noise immunity enhancement.

 

 

 

 

10

RGND

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

 

11

SS

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

 

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

 

 

 

 

12

VSNS

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

 

 

 

 

 

13

PGOOD

Power Good Indicator Output. Active high open drain output.

 

14

UGATE2

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 MOSFET.

 

 

 

 

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

 

www.richtek.com

DS8812A-04 November 2013

2

 

Richtek RT8812AGQW Schematic

 

 

RT8812A

 

 

 

Pin No.

Pin Name

Pin Function

15

BOOT2

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

 

 

Switch Node for PWM2. This pin is return node of the high side driver of PWM 2.

16

PHASE2

Connect this pin to the Source of high side MOSFET together with the Drain of

 

 

low side MOSFET and the inductor.

17

LGATE2

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 MOSFET.

 

 

18

PVCC

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

bypass capacitor from this pin to GND.

 

 

19

LGATE1

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 MOSFET.

 

 

 

 

Switch Node for PWM1. This pin is return node of the high side driver of PWM 1.

20

PHASE1

Connect this pin to the Source of high side MOSFET together with the Drain of

 

 

low side MOSFET and the inductor.

21 (Exposed Pad)

GND

Ground. The Exposed pad should be soldered to a large PCB and connected to

GND for maximum thermal dissipation.

 

 

Function Block Diagram

 

VREF

 

 

 

 

 

 

 

 

 

 

 

 

 

Reference

 

 

 

 

 

 

VID

 

 

 

Output Gen.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

REFADJ

 

 

 

 

 

 

 

 

 

PVCC

 

 

 

 

Power On Reset

 

 

 

 

PSI

 

 

Mode Select

 

 

 

 

 

OV

 

 

 

& Central Logic

 

 

 

 

REFIN

 

 

-

 

 

 

 

 

PGOOD

Threshold

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Select

 

 

+

 

 

 

 

 

 

 

UV

 

 

Control & Protection Logic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

40% REFIN

 

+

 

 

Boot-Phase

 

 

 

 

 

 

-

 

 

Detection 1

 

 

 

Soft-Start

 

PWM

 

 

Boot-Phase

 

 

 

& Slew Rate

 

CMP

 

 

Detection 2

 

 

SS

Control

 

 

 

 

 

 

 

 

 

 

+

TON

 

 

 

 

BOOT1

VSNS

 

 

 

-

 

 

 

 

UGATE1

 

 

 

Gen 1

 

 

 

 

RGND

 

 

 

 

 

 

PWM1

 

 

PHASE1

 

Enable

 

To Driver Logic

 

 

 

 

LGATE1

EN

 

 

 

 

 

 

Logic

 

To Power On Reset

 

 

 

Driver

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TON

 

PWM2

Logic

 

BOOT2

 

 

 

 

 

 

 

 

UGATE2

 

 

 

 

 

Gen 2

 

 

 

 

 

 

 

 

 

 

 

 

 

PHASE2

 

 

 

 

 

 

 

 

 

 

 

To Power On Reset

 

 

 

 

 

 

LGATE2

 

 

 

 

 

 

 

 

TON

VIN

 

 

 

 

 

 

 

-

 

Detection

 

 

 

 

 

 

S/H

 

 

 

 

 

 

 

Current

 

GM+

VB

 

PHASE1

ZCD

To Driver Logic

 

Balance

 

S/H

-

 

 

 

 

 

VB

 

 

 

 

To Protection Logic

Current

 

GM+

 

 

 

 

 

 

 

 

 

 

 

 

Limit

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8812A-04 November 2013

www.richtek.com

 

3

RT8812A

Operation

The RT8812A is a 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 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 range and output voltage. Another one-shot sets a minimum off-time.

The RT8812A 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 pin to the GND will be charged by a current source and determines the soft-start time.

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 RT8812A implements internal current balance mechanism in the current loop. The RT8812A 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.

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 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 VREFIN 1.33V, OV = 2V, or VREFIN > 1.33V, OV = 1.5 x VREFIN), 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.

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS8812A-04 November 2013

4

 

 

 

 

 

 

RT8812A

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

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

 

 

 

 

 

−0.3V to 30V

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

 

 

 

 

 

−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, PD @ TA = 25°C

 

 

 

 

 

 

 

WQFN-20L 3x3 -------------------------------------------------------------------------------------------------------------

 

 

 

 

 

3.33W

 

Package Thermal Resistance

(Note 2)

 

 

 

 

 

 

 

WQFN-20L 3x3, θJA --------------------------------------------------------------------------------------------------------

 

 

 

 

 

30°C/W

 

WQFN-20L 3x3, θJC -------------------------------------------------------------------------------------------------------

 

 

 

 

 

7.5°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)

 

 

 

 

 

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

 

 

 

 

 

7V to 26V

Supply Voltage, VPVCC ----------------------------------------------------------------------------------------------------

 

 

 

 

 

4.5V to 5.5V

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

--

5.5

 

V

PVCC Supply Current

ISUPPLY

EN = 3.3V, Not Switching

--

1.5

2

 

mA

PVCC Shutdown Current

ISHDN

EN = 0V

 

--

--

10

 

A

PVCC POR Threshold

 

 

 

3.8

4.1

4.4

 

V

 

 

 

 

 

 

 

 

 

POR Hysteresis

 

 

 

--

0.3

--

 

V

Switching Frequency

fSW

RTON = 500k

(Note 5)

270

300

330

 

kHz

 

 

 

 

 

 

 

 

 

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8812A-04 November 2013

www.richtek.com

 

5

RT8812A

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

Minimum On-Time

tON(MIN)

 

--

70

--

ns

Minimum Off-Time

tOFF(MIN)

 

--

300

--

ns

EN Input Voltage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EN Input Voltage

Logic-High

VENH

 

1.6

--

--

V

Logic-Low

VENL

 

--

--

0.8

 

 

 

Mode Decision

 

 

 

 

 

 

PSI High Threshold

VPSIH

Enables Two Phases with FCCM

2.4

--

--

V

PSI Intermediate Threshold

VPSIM

Enables One Phases with FCCM

1.2

--

1.8

V

PSI Low Threshold

VPSIL

Enables One Phases with DEM

--

--

0.8

V

VID Input Voltage

High-Level

VVIDH

 

2

--

--

V

Low-Level

VVIDL

 

--

--

1

 

 

 

Protection Function

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Zero Current Crossing

 

 

 

8

--

8

mV

Threshold

 

 

 

 

 

 

 

 

 

 

Current Limit Setting Current

 

IOCSET

 

9

10

11

A

 

 

 

 

 

 

 

 

Current Limit Setting Current

 

IOCSET_TC

 

--

6300

--

ppm/ C

Temperature Coefficient

 

 

 

 

 

 

 

Current Limit Threshold

 

 

ROCSET = 10k

--

60

--

mV

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

 

OV Fault Delay

 

 

FB forced above OV threshold

--

5

--

s

Relative Under Voltage

 

VUVP

UVP

35

40

45

%

Protection Threshold

 

UV Fault Delay

 

 

FB forced above UV threshold

--

3

--

s

 

 

 

 

 

 

 

 

Thermal Shutdown Threshold

 

TSD

 

--

150

--

C

PGOOD Blanking Time

 

 

From EN = high to PGOOD = high

--

2.5

--

ms

(Internal)

 

 

with VSNS within regulation point

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

From first UGATE to VSNS

 

 

 

 

VSNS Soft-Start (Internal)

 

 

regulation point, VREFIN = 1V and

--

0.7

--

ms

 

 

 

 

VSNS initial = 0V

 

 

 

 

Soft-Start Current Source

 

ISS

 

--

5

--

A

Error Amplifier

 

 

 

 

 

 

VSNS Error Comparator

 

 

VREFIN = 1V

17.5

12.5

7.5

mV

Threshold (Valley)

 

 

 

 

 

 

 

 

 

Reference

 

 

 

 

 

 

Reference Voltage

 

VVREF

Sourcing Current = 1mA, VID no

1.98

2

2.02

V

 

Switching

Copyright ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS8812A-04 November 2013

6

 

RT8812A

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

Driver On-Resistance

 

 

 

 

 

 

 

 

 

 

 

 

 

UGATE Driver Source

RUGATEsr

BOOTx PHASEx Forced to 5V

--

2

4

 

UGATE Driver Sink

RUGATEsk

BOOTx PHASEx Forced to 5V

--

1

2

 

LGATE Driver Source

RLGATEsr

LGATEx, High State

--

1.5

3

 

LGATE Driver Sink

RLGATEsk

LGATEx, Low State

--

0.7

1.5

 

 

 

From LGATE Falling to UGATE

--

30

--

 

 

 

Rising

 

Dead-Time

 

 

 

 

ns

 

From UGATE Falling to LGATE

--

20

--

 

 

 

 

 

Rising

 

 

 

 

 

 

 

Internal Boost Charging

RBOOT

PVCC to BOOTx, IBOOT = 10mA

--

40

80

 

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. 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 ©2013 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8812A-04 November 2013

www.richtek.com

 

7

+ 15 hidden pages