Richtek RT8805CGQV, RT8805CGQVA, RT8805CPQV, RT8805CPQVA Schematic [ru]

Preliminary

RT8805C

Two Phase General Purpose PWM Controller

General Description

The RT8805C is the most compact dual-phase

synchronous buck controller in the industry specifically

designed for high power density applications. This part is

capable of delivering up to 60A output current due to its

embedded bootstrapped drivers that support 12V + 12V

driving capability.

The phase currents are sensed by innovative time sharing

current sensing technique for current balance and

DS(ON)

over current balance. Using one common GM amplifier to

sense two phase currents eliminates offset and

nonlinearity of the GM amplifier and yields good current

balance. Other features include adjustable operation

frequency from 50kHz to 1MHz, adjustable soft-start,

PGOOD, external compensation, enable/shutdown for

various application and performance consideration.

The RT8805C comes to a tiny footprint package of

VQFN-16L 3x3 package that is capable of dissipating up

to 1.47W heat.

Ordering Information

RT8805C

Features

12V Power Supply Voltage

z 2 Phase Power Conversion

z Embedded 12V Boot Strapped Driver

z Precise Core Voltage Regulation

z Low Side MOSFET R

Current Sensing for

DS(ON)

Power Stage Current Balance

z External Compensation

z Adjustable Soft-Start

z Adjustable Frequency and Typical at 300kHz Per

Phase

z Power Good Indication

z Adjustable Over Current Protection

z Small 16-Lead VQFN Package

z RoHS Compliant and 100% Lead (Pb)-Free

Applications

z Middle-High End GPU Core Power

z High End Desktop PC Memory Core Power

z Low Output Voltage, High Power Density DC-DC

Converters

z Voltage Regulator Modules

Package Type QV : VQFN-16L 3x3 (V-Type)

Operating Temperature Range P : Pb Free with Commercial Standard

Note :

RichTek Pb-free 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.

`100% matte tin (Sn) plating.

Marking Information

For marking information, contact our sales representative

directly or through a RichTek distributor located in your

area, otherwise visit our website for detail.

Pin Configurations

(TOP VIEW)

PHASE1

LGATE1

UGATE1

BOOT1

AGND

IMAX

GND

VQFN-16L 3x3

VCC

13141516

COMP

LGATE2

PHASE2

UGATE2

BOOT2

PGOOD

8765

DS8805C-01 November 2005 www.richtek.com

RT8805C

Typical Application Circuit

Preliminary

3.3V

12V

Function Block Diagram

PGOOD

VCC

IMAX

AGND

COMP

GND

RT8805C

BOOT1

UGATE1

PHASE1

LGATE1

BOOT2

UGATE2

PHASE2

LGATE2

OUT

PGOOD

COMP

AGND

IMAX

VCC

0.8V

External

Soft Star

Reg

Clock

CLK1 CLK2

Current

Balance

OCP

PWMCP

RAMP2RAMP1

S/H

PWM1

Logic

PWM2

Logic

CLK2CLK1

MUX

PGOOD

PHASE2 PHASE1

To PWM Logic

Central

Logic

BOOT1

UGATE1

PHASE1

LGATE1

BOOT2

UGATE2

PHASE2

LGATE2

GND

DS8805C-01 November 2005www.richtek.com

Functional Pin Description

Preliminary

RT8805C

UGA TE1 (Pin 1), UGA TE2 (Pin 11)

Upper Gate Drive. These pins drive the gates of the highside

MOSFETs.

BOOT1 (Pin 2), BOOT2 (Pin 10)

Bootstrap Power Pin. These pins power the high-side

MOSFET drivers. Connect These pins to the junctions of

the bootstrap capacitors.

AGND (Pin 3)

Chip Analog Ground.

IMAX (Pin 4)

Maximum Current Setting. This pin sets the current limiting

level. Connect this pin with resistor to ground to set the

current limit.

RT (Pin 5)

Timing Resistor. Connect a resistor from RT to AGND to

set the clock frequency.

PHASE1 (Pin 16), PHASE2 (Pin 12)

These pins are return nodes of the high-side driver.

Connect These pins to high-side MOSFET sources

together with the low-side MOSFET drains and the

inductors.

VCC (Pin 14)

The VCC pin is the external 12V power. Internal 5V power

(VDD) is regulated from this pin. This pin also powers the

low side MOSFETS drivers.

GND (Exposed Pad)

Exposed pad should be soldered to PCB board and

connected to GND.

SS (Pin 6)

Soft-Start Pin. This pin provides soft-start function for

controller. The COMP voltage of the converter follows the

ramping voltage on the SS pin.

COMP (Pin 7)

Compensation Pin. This pin is output node of the error

amplifier.

FB (Pin 8)

Feedback Pin. This pin is negative input pin of the error

amplifier.

PGOOD (Pin 9)

Power Good. PGOOD is an open drain output used to

indicate the status of the voltages on SS pin and FB pin.

PGOOD will go high impedance when SS > 3.7V and FB

> 0.6V.

LGA TE1 (Pin 15), LGA TE2 (Pin 13)

Lower Gate Drive. These pins drive the gate of the lowside

MOSFETs.

DS8805C-01 November 2005 www.richtek.com

RT8805C

Preliminary

Absolute Maximum Ratings (Note 1)

z Supply Voltage, V

z PHASE to GND

-------------------------------------------------------------------------------------------------- −0.3V to 16V

DC------------------------------------------------------------------------------------------------------------------------- −5V to 15V

< 200ns ------------------------------------------------------------------------------------------------------------------ −10V to 30V

z BOOT to PHASE ------------------------------------------------------------------------------------------------------ 15V

z BOOT to GND

DC------------------------------------------------------------------------------------------------------------------------- −0.3V to VCC+15V

< 200ns ------------------------------------------------------------------------------------------------------------------ −0.3V to 42V

z Input, Output or I/O Voltage ----------------------------------------------------------------------------------------- GND-0.3V to 7V

z Power Dissipation, P

@ T

= 25°C

VQFN−16L 3x3 --------------------------------------------------------------------------------------------------------- 1.47W

z Package Thermal Resistance (Note 4)

VQFN−16L 3x3, θJA--------------------------------------------------------------------------------------------------- 68°C/W

z Junction Temperature ------------------------------------------------------------------------------------------------- 150°C

z Lead Temperature (Soldering, 10 sec.)--------------------------------------------------------------------------- 260°C

z ESD Susceptibility (Note 2)

HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 1.5kV

MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V

Recommended Operating Conditions (Note 3)

z Supply Voltage --------------------------------------------------------------------------------------------------------- 9V to 14V

z Junction Temperature Range ---------------------------------------------------------------------------------------- −20°C to 70°C

Electrical Characteristics

= 12V, TA = 25°C, unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Units

Supply Input

Power Supply Voltage VCC -- 12 15 V

Power On Reset VCC 5.4 5.9 6.5 V

Power On Reset Hysteresis -- 0.3 -- V

Power Supply Current I

Soft Start

Soft Start Current ISS 8 10 15 μA

Oscillator

Free Running Frequency f

Frequency Variation -15 -- 15 %

Frequency Range 50 300 1000 kHz

Maximum Duty Cycle 70 75 80 %

VSS = 0V -- 10 -- mA

VCC

RT = 33kΩ 255 300 345 kHz

OSC

To be continued

DS8805C-01 November 2005www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Units

Reference Voltage

Preliminary

RT8805C

Feedback Voltage VFB V

= 0.8V 0.784 0.8 0.816 V

Error Amplifier

DC Gain 60 70 -- dB

Gain-Bandwidth Product GBW

Trans-conductance GM

MAX Current (Source & Sink)

COMP

LOAD

COMP

= 5pF

= 20kΩ

= 2.5V

6 10 -- MHz

600 660 --

300 360 --

μA/V

μA

Current Sense GM Amplifier

PHASE

IMAX

= 33kΩ

-- -220 -- mV

Gate Driver

Maximum Upper Drive Source I

Upper Drive Sink R

Maximum Lower Drive Source I

Lower Drive Sink R

UGATE(MAX)

UGATE

LGATE(MAX)

LGATE

BOOT − PHASE = 12V 1 -- -- A

= 1V -- 3.5 7 Ω

UGATE

PVCC = 12V 1 -- -- A

= 1V -- 2 4 Ω

LGATE

Protection

Under Voltage Protection 0.55 0.6 0.65 V

Power Sequence

Power Good Threshold 3.4 3.7 4 V

Power Good Sink Capability (4mA) -- 0.05 0.2 V

Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for

stress ratings. 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 for extended

periods may remain possibility to affect device reliability.

Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions.

Note 4. θ

is measured in the natural convection at TA = 25°C on a low effective thermal conductivity test board of

JEDEC 51-3 thermal measurement standard.

DS8805C-01 November 2005 www.richtek.com

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