SMH4812
Preliminary
PIN CONFIGURATION
DRAIN SENSE
VGATE
EN/TS
PD1#
PD2#
FAULT#
CBSENSE
V
SS
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
DD
PG#
ENPG
FS#
2.5V
REF
5V
REF
OV
UV
2055 PCon 2.0
PIN DESCRIPTIONS
DRAIN SENSE (1)
The DRAIN SENSE input monitors the voltage at the drain
of the external power MOSFET switch with respect to V
SS
.
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
they are at V
SS
. These pins each have an internal 50kW
pull-up to 5V.
CBSENSE (7)
The circuit breaker sense input is used to detect over-
current conditions across an external, low value sense
resistor (R
S
) tied in series with the Power MOSFET. A
voltage drop of greater than 50mV across the resistor for
longer than t
CBD
will trip the circuit breaker. A program-
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.
The reference output is with respect to V
SS
.
2.5VREF (12)
This is a precision 2.5V output reference voltage that may
be used to expand the logic input functions on the
SMH4812. The reference output is with respect to V
SS
.
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.
SUMMIT MICROELECTRONICS, Inc.
2055 4.1 03/27/09
3
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
