RT9228GS datasheet(5/8 Pages) RICHTEK

5 / 8 page

RT9228

DS9228-06

March 2007

www.richtek.com

Functional Pin Description

VCC (Pin 1)

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

also provides the gate bias charge for all the MOSFETs

controlled by the IC.

VID0, VID1, VID2, VID3, VID4 (Pin 6, 5, 4, 3, and 2)

VIDO-4 are the input pins to the 5-bit DAC. The states of

these five pins program the internal voltage reference,

DACOUT. The level of DACOUT sets the core converter

output voltage. It also sets the core PGOOD and OVP

thresholds. Table 1 specifies the DACOUT voltage of 32

combinations of VID levels.

PGOOD (Pin 7)

PGOOD is an open collector output used to indicate the

status of the output voltage. This pin is pulled low when

the core output is not within ±10% of the DACOUT

reference voltage and the other outputs are below their

under-voltage thresholds.

The PGOOD output is open for

'11111' V

ID codes that

inhibit operation. See table 1.

FAULT (Pin 8)

This pin is low during normal operation, but it is pulled to

about 8V (VCC = 12V) in the event of an over-voltage or

over-current condition.

SS (Pin 9)

Connect a capacitor from this pin to ground. This capacitor,

along with an internal 11

μA (VSS >1V) current source, sets

the soft-start interval of the converter.

FB2 (Pin 11)

Connect this pin to VOUT2 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 2.55V

(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 the gate of an external MOSFET or the

base of an NPN. This pin provides the drive for the linear

controller's pass transistor.

FB3 (Pin 16)

Connect this pin to VOUT3 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. ROCSET1, 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 :

(ON)

OCSET1

PEAK

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

Sustaining an over-current for 2 soft-start intervals shuts

down the controller.

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