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RT9238

VRM8.5 PWM and Triple Linear Power System Controller

Richtek Technology 

RT9238

Preliminary

VAUX (Pin 16)

This pin provides boost current for the three linear

regulator output drives in the event bipolar NPN

transistors (instead of N-channel MOSFETs) are

employed as pass elements. The voltage at this pin

is monitored for power-on reset (POR) purpose.

GND (Pin 17)

Signal ground for the IC. All voltage levels are

measured with respect to this pin.

DRIVE3 (Pin 18)

Connect this pin to the gate of an external MOSEFT.

This pin provides the drive for the 1.5V regulator’s

pass transistor.

VSEN3 (Pin 19)

Connect this pin to the output of the 1.5V linear

regulator. This pin is monitored for under-voltage

events.

ICOMP (Pin 20)

This pin is non-inverting input of the PWM error

amplifier. It determine the VOUT1 voltage. Connect a

resistor (RF) to VDAC pin. A sense current of lower

MOSFET is fed to this pin to pull low the DACOUT

voltage. (see VDAC)

VDAC (Pin 21)

This pin is internal DAC buffer output. Connect a

resistor(RF) from this pin to ICOMP pin. The resistor

provide a voltage drop rated from lower MOSFET

turn on voltage drop. A sample hold circuit sense the

voltage drop of lower MOSFET(IL x RDSON ) when

LGATE1 turn on. The ratio is :

(IL x RDSON ) x RF/3k

FB1 (Pin 22)

This pin is connected to the PWM converter’s output

voltage. This pin also connects to internal PWM error

amplifier inverting input and power good monitor.

OCSET1 (Pin 23)

Connect a resistor from this pin to the drain of the

respective upper MOSFET. This resistor, an internal

200µA current source, and the upper MOSFET on-

resistance set the converter over-current trip point.

An over-current trip cycles the soft-start function. The

voltage at this pin is monitored for power-on reset

(POR) purpose and pulling this pin low with an open

drain device will shut down the IC.

PGND (Pin 24)

This is the power ground of UGATE1&LGATE1. Tie

the synchronous PWM converter’s lower MOSFET

source to this pin.

LGATE1 (Pin 25)

Connect LGATE1 to the PWM converter’s lower

MOSFET gate. This pin provides the gate drive for

the lower MOSFET.

PHASE1 (Pin 26)

This pin is used to monitor the voltage drop across

the upper MOSFET for over-current protection. This

pin is also used to sense lower MOSFET voltage

drop for VOUT1 voltage droop tuning.

UGATE1 (Pin 27)

Connect UGATE1 pin to the PWM converter’s upper

MOSFET gate. This pin provides the gate drive for

the upper MOSFET.

VCC (Pin 28)

Provide a 12V supply voltage for the IC to this pin.

This pin also provides the gate bias charge for all the

MOSFETs controlled by the IC. The voltage at this

pin monitored for power-on reset (POR) purpose.

www.richtek-ic.com.tw

10

DS9238-01 July 2001

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