LTC1647-1/
LTC1647-2/LTC1647-3
8
1647fa
PIN FUNCTIONS
V
CC1
(LTC1647-3): Channel 1 Positive Supply Input.
The supply range for normal operation is 2.7V to 16.5V.
The supply current, I
CC1
, is typically 1mA. Channel 1’s
undervoltage lockout (UVLO) circuit disables GATE 1 until
the supply voltage at V
CC1
is greater than V
LKO
(typically
2.45V). GATE 1 is held at ground potential until UVLO
deactivates. If ON1 is high and V
CC1
is above the UVLO
threshold voltage, GATE 1 is pulled high by a 10μA current
source. If V
CC1
falls below (V
LKO
– V
LKH
), GATE 1 is pulled
immediately to ground. The internal reference and the
common charge pump are powered from the higher of
the two V
CC
inputs, V
CC1
or V
CC2
.
V
CC2
(LTC1647-3): Channel 2 Positive Supply Input. See
V
CC1
for functional description.
V
CC
: The Common Positive Supply Input for the LTC1647-1
and the LTC1647-2. V
CC1
and V
CC2
are internally connected
together.
GND: Chip Ground.
ON1: Channel 1 ON Input. The threshold at the ON1 pin is
set at 1.29V with 70mV hysteresis. If UVLO and the circuit
breaker of channel 1 are inactive, a logic high at ON1 enables
the 10μA charge pump current source, pulling the GATE
1 pin above V
CC1
. If the ON1 pin is pulled low, the GATE 1
pin is pulled to ground by a 50μA current sink.
ON1 resets channel 1’s electronic circuit breaker by pulling
ON1 low for greater than one t
RESET
period (50μs). A
low-to-high transition at ON1 restarts a normal GATE 1
pull-up sequence.
ON2: Channel 2 ON Input. See ON1 for functional
description.
FAULT1: Channel 1 Open-Drain Fault Status Output. FAULT1
pin pulls low after 0.3μs (t
FAULT
) if the circuit breaker
measures greater than 50mV across the sense resistor
connected between V
CC1
and SENSE 1. If FAULT1 pulls
low, GATE 1 also pulls low. FAULT1 remains low until ON1
is pulled low for at least one t
RESET
period.
FAULT2: Channel 2 Open-Drain Fault Status Output. See
FAULT 1 for functional description.
SENSE1: Channel 1 Circuit Breaker Current Sense Input.
Load current is monitored by a sense resistor connected
between V
CC1
and SENSE 1. The circuit breaker trips if the
voltage across the sense resistor exceeds 50mV (V
CB
). To
disable the circuit breaker, connect SENSE 1 to V
CC1
. In
order to obtain optimum performance, use Kelvin-sense
connections between the V
CC
and SENSE pins to the
current sense resistor.
SENSE2: Channel 2 Circuit Breaker Current Sense Input.
See SENSE 1 for functional description.
GATE1: Channel 1 N-channel MOSFET Gate Drive Output.
An internal charge pump guarantees at least 10V of gate
drive from a 5V supply. Two Zener clamps are incorporated
at the GATE 1 pin; one Zener clamps GATE 1 approximately
15V above V
CC
and the second Zener clamps GATE 1
appoximately 28V above GND. The rise time at GATE 1 is
set by an external capacitor connected between GATE 1
and GND and an internal 10μA current source provided
by the charge pump. The fall time at GATE 1 is set by
the 50μA current sink if ON1 is pulled low. If the circuit
breaker is tripped or the supply voltage hits the UVLO
threshold, a 50mA current sink rapidly pulls GATE 1 low.
An external 23V Zener from GATE1 to GND is required for
supply voltages (V
CC1
) greater than 10V.
GATE2: Channel 2 N-channel MOSFET Gate Drive Output.
See GATE 1 for functional description.
NC: No Connection.
