SC1155

PROGRAMMABLE SYNCHRONOUS

DC/DC HYSTERETIC CONTROLLER

WITH VRM 9.0 VID RANGE

© 2000 SEMTECH CORP.

PRELIMINARY - August 7, 2000

3

PIN DESCRIPTION

Pin

Pin Name Pin Function

1

IOUT

Current Out. The output voltage on this pin is proportional to the load current as measured

across the high side MOSFET, and is approximately equal to 2 x R

2

DROOP

Droop Voltage. This pin is used to set the amount of output voltage set-point droop as a

function of load current. The voltage is set by a resistor divider between IOUT and AGND.

3

OCP

Over Current Protection. This pin is used to set the trip point for over current protection by a

resistor divider between IOUT and AGND.

4

VHYST

Hysteresis Set Pin. This pin is used to set the amount of hysteresis required by a resistor

divider between VREFB and AGND.

5

VREFB

Buffered Reference Voltage (from VID circuitry).

6

VSENSE

Output Voltage Sense.

7

AGND

Small Signal Analog and Digital Ground.

8

SOFTST

Soft Start. Connecting a capacitor from this pin to AGND sets the time delay.

9

NC

Not connected

10

LODRV

Low Drive Control. Connecting this pin to +5V enables normal operation. When LOHIB is

grounded, this pin can be used to control LOWDR.

11

LOHIB

Low Side Inhibit. This pin is used to eliminate shoot-thru current.

12

DRVGND Power Ground. Insure output capacitor ground is connected to this pin.

13

LOWDR

Low Side Driver Output. Connect to gate of low side MOSFET.

14

DRV

Drive Regulator for the MOSFET Drivers.

15

VIN12V

12V Supply. Connect to 12V power rail.

16

BOOT

Bootstrap. This pin is used to generate a floating drive for the high side FET driver.

17

HIGHDR

High Side Driver Output. Connect to gate of high side MOSFET.

18

BOOTLO Bootstrap Low. In desktop applications, this pin connects to DRVGND.

19

HISENSE High Current Sense. Connected to the drain of the high side FET, or the input side of a current

sense resistor between the input and the high side FET.

20

LOSENSE Low Current Sense. Connected to the source of the high side FET, or the FET side of a current

sense resistor between the input and the high side FET.

21

IOUTLO

This is the sampling capacitors bottom leg. Voltage on this pin is voltage on the LOSENSE pin

when the high side FET is on.

22

INHIBIT

Inhibit. If this pin is grounded, the MOSFET drivers are disabled. Usually connected to +5V

through a pull-up resistor.

23

VID4

(1)

Programming Input (MSB).

24

VID3

(1)

Programming Input.

25

VID2

(1)

Programming Input.

26

VID1

(1)

Programming Input.

27

VID0

(1)

Programming Input (LSB).

28

PWRGD

(1)

Power Good. This open collector logic output is high if the output voltage is within 5% of the set

point.