5
LT1640L/LT1640H
1640lhfb
PIN FUNCTIONS
UUU
UV (Pin 3): Analog Undervoltage Input. When UV is
pulled below the 1.223V high to low threshold, an under-
voltage condition is detected and the GATE pin will be
immediately pulled low. The GATE pin will remain low
until UV rises above the 1.243 low to high threshold.
The UV pin is also used to reset the electronic circuit
breaker. If the UV pin is cycled low and high following the
trip of the circuit breaker, the circuit breaker is reset and
a normal power-up sequence will occur.
V
EE
(Pin 4): Negative Supply Voltage Input. Connect to
the lower potential of the power supply.
SENSE (Pin 5): Circuit Breaker Sense Pin. With a sense
resistor placed in the supply path between V
EE
and
SENSE, the circuit breaker will trip when the voltage
across the resistor exceeds 50mV. Noise spikes of less
than 2µs are filtered out and will not trip the circuit
breaker.
If the circuit breaker trip current is set to twice the normal
operating current, only 25mV is dropped across the
sense resistor during normal operation. To disable the
circuit breaker, V
EE
and SENSE can be shorted together.
GATE (Pin 6): Gate Drive Output for the External
N-Channel. The GATE pin will go high when the following
start-up conditions are met: the UV pin is high, the OV pin
is low and (V
SENSE
– V
EE
) < 50mV. The GATE pin is pulled
high by a 45µA current source and pulled low with a
50mA current source.
DRAIN (Pin 7): Analog Drain Sense Input. Connect this
pin to the drain of the external N-channel and the V
–
pin
of the power module. When the DRAIN pin is below V
PG
,
the PWRGD or PWRGD pin will toggle.
V
DD
(Pin 8): Positive Supply Voltage Input. Connect this
pin to the higher potential of the power supply inputs and
the V
+
pin of the power module. The input supply voltage
ranges from 10V to 80V.
BLOCK DIAGRA
W
–
+
–
+
+
–
+
–
DRAIN
1640 BD
GATESENSEV
EE
V
EE
V
PG
OUTPUT
DRIVE
PWRGD/PWRGD
50mV
V
CC
V
DD
REF
REF
UV
OV
LOGIC
AND
GATE DRIVE
V
CC
AND
REFERENCE
GENERATOR
–
+
–
+
