RT9228CS datasheet(5/10 Pages) RICHTEK

5 / 10 page

RT9228

DS9228-03 July 2001

www.richtek.com

FB2 (Pin 11)

Connect this pin to a resistor divider to set the linear

regulator output voltage. VIN2 (Pin 12) this pin

supplies power to the internal regulator. Connect this

pin to a suitable 3.3V source.

Additionally, this pin is used to monitor the 3.3V

supply. If, following a startup cycle, the voltage drops

below 2.8V (typically), the chip shuts down. A new

soft-start cycle is initiated upon return of the 3.3V

supply above the under-voltage threshold.

VOUT2 (Pin 13)

Output of the linear regulator. Supplies current up to

230mA.

GND (Pin 14)

Signal ground for the IC. All voltage levels are

measured with respect to this pin.

GATE3 (Pin 15)

Connect this pin to drive gate of an external

MOSFET or NPN. This pin provides the drive for the

linear controller’s pass transistor.

FB3 (Pin 16)

Connect this pin to a resistor divider to set the linear

controller output voltage.

FB1 (Pin 18)

The FB1 pin is the inverting input of the error

amplifier.

VSEN1 (Pin 19)

This pin is connected to the PWM converter’s output

voltage. The PGOOD and OVP comparator circuits

use this signal to report output voltage status and for

over voltage protection.

OCSET1 (Pin 20)

Connect a resistor (ROCSET1) from this pin to the

drain of the upper MOSFET. ROCSET, an internal

200

µA current source (IOCSET1), and the upper

MOSFET on-resistance (RDS(ON)) set the PWM

converter over-current (OC) trip point according to

the following equation:

IOCSET1×ROCSET1

IPEAK =

RDS (ON)

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

Sustaining an over-current for 2 soft-start intervals

shuts down the controller.

PGND (Pin 21)

This is the power ground of UGATE1 and LGATE1.

Tie the PWM converter’s lower MOSFET source to

this pin.

LGATE1 (Pin 22)

Connect LGATE1 to the PWM converter’s lower

MOSFET gate. This pin provides the gate drive for

the lower MOSFET.

PHASE1 (Pin 23)

Connect the PHASE1 pin to the PWM converter’s

upper MOSFET source. This pin is used to monitor

the voltage drop across the upper MOSFET for over-

current protection.

UGATE1 (Pin 24)

Connect UGATE1 pin to the PWM converter’s upper

MOSFET gate. This pin provides the gate drive for

the upper MOSFET.

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