3

2055 4.0 12/22/00

SMH4812

SUMMIT MICROELECTRONICS, Inc.

Preliminary

PIN CONFIGURATION

PIN DESCRIPTIONS

DRAIN SENSE (1)

The DRAIN SENSE input monitors the voltage at the drain

An internal 10µA source pulls the DRAIN SENSE signal

towards the 5V reference level. DRAIN SENSE must be

held below 2.5V to enable the PG outputs.

EN/TS (3)

The Enable/Temperature Sense input is the master en-

able input. If EN/TS is less than 2.5V, VGATE will be

disabled. This pin has an internal 200kW pull-up to 5V.

PD1#, PD2# (4, 5)

These are logic level active low inputs that can optionally

be employed to enable VGATE and the PG outputs when

pull-up to 5V.

CBSENSE (7)

The circuit breaker sense input is used to detect over-

current conditions across an external, low value sense

voltage drop of greater than 50mV across the resistor for

mable Quick-Trip sense point is also available.

UV (9)

The UV pin is used as an under-voltage supply monitor,

typically in conjunction with an external resistor ladder.

VGATE will be disabled if UV is less than 2.5V. Program-

mable internal hysteresis is available on the UV input,

adjustable in increments of 62.5mV. Also available is a

filter delay on the UV input.

OV (10)

The OV pin is used as an over-voltage supply monitor,

typically in conjunction with an external resistor ladder.

VGATE will be disabled if OV is greater than 2.5V. A filter

delay is available on the OV input.

VGATE (2)

The VGATE output activates an external power MOSFET

switch. This signal supplies a constant current output

(100µA typical), which allows easy adjustment of the

MOSFET turn on slew rate.

FAULT# (6)

FAULT# is an open-drain, active-low output that indicates

the fault status of the device.

5VREF (11)

This is a precision 5V output reference voltage that may be

used to expand the logic input functions on the SMH4812.

2.5VREF (12)

This is a precision 2.5V output reference voltage that may

be used to expand the logic input functions on the

FS# (13)

The Forced Shutdown (FS#) pin is an active low input that

causes VGATE and PG outputs to be shut down at any

time after an internal hold-off timer has expired. The hold-

off timer allows supervisory circuits on the secondary side

(which are not powered up initially) to control shut down of

the SMH4812 via an opto-isolator. This input has no pull-

up resistor.

DRAIN SENSE

VGATE

EN/TS

PD1#

PD2#

FAULT#

CBSENSE

PG#

ENPG

FS#

OV

UV

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

2055 PCon 2.0