8
LTC4244/LTC4244-1
42441f
RESETOUT (Pin 10): Open-Drain Digital Output. Connect
the CPCI_LOCAL_RST# signal to the RESETOUT pin.
RESETOUT is the logical combination of the RESETIN and
PWRGD.
DRIVE (Pin 11): Precharge Base Drive Output. Provides
base drive for an external NPN emitter-follower that in turn
biases the PRECHARGE node.
PRECHARGE (Pin 12): Precharge Monitor Input. An inter-
nal error amplifier servos the DRIVE pin voltage to keep the
PRECHARGE node at 1V. See Applications Information for
generating voltages other than 1V. If not used, tie the
PRECHARGE pin to ground.
5V
IN
(Pin 13): 5V Supply Sense Input. An undervoltage
lockout circuit prevents the switches from turning on
when the voltage at the 5V
IN
pin is less than 4.25V.
5V
SENSE
(Pin 14): 5V Current Limit Sense. With a sense
resistor placed in the supply path between 5V
IN
and
5V
SENSE
, the GATE pin voltage will be adjusted to maintain
a constant 51mV across the sense resistor and a constant
current through the switch while the TIMER pin is low. A
foldback feature makes the current limit decrease as the
voltage at the 5V
OUT
pin approaches GND. When the
TIMER pin is high, the circuit breaker function is enabled.
If the voltage across the sense resistor exceeds 52mV, the
circuit breaker is tripped after a 25µs time delay. In the
event of a short-circuit or large overcurrent transient
condition, the GATE pin voltage will be adjusted to main-
tain a constant 150mV across the sense resistor and a
constant current through the switch.
GATE (Pin 15): High Side Gate Drive for the External 3.3V
and 5V N-Channel Pass Transistors. An external series RC
network is required for current limit loop compensation
and setting the minimum ramp-up time. During power-up,
the slope of the voltage rise at the GATE is set by the 67µA
current source connected through a Schottky diode to
12V
IN
and the external capacitor connected to GND (C1 in
Figure 1) or by the 3.3V or 5V current limit and the bulk
capacitance in the 3.3V
OUT
or 5V
OUT
supply lines. During
power down, the slew rate of the GATE voltage is set by the
60µA current source connected to GND and the external
GATE capacitor (C1 in Figure 1).
The voltage at the GATE pin will be modulated to maintain
a constant current when either the 5V or 3.3V supplies go
into current limit. In the event of an overcurrent fault, the
GATE pin is immediately pulled to GND.
3.3V
SENSE
(Pin 16): 3.3V Current Limit Sense. With a
sense resistor placed in the supply path between 3.3V
IN
and 3.3V
SENSE
, the GATE pin voltage will be adjusted to
maintain a constant 51mV across the sense resistor and a
constant current through the switch while the TIMER pin
is low. A foldback feature makes the current limit decrease
as the voltage at the 3.3V
OUT
pin approaches GND. When
the TIMER pin is high, the circuit breaker function is
enabled. If the voltage across the sense resistor exceeds
52mV, the circuit breaker is tripped after a 25µs time delay.
In the event of a short-circuit or large overcurrent transient
condition, the GATE pin voltage will be adjusted to main-
tain a constant 150mV across the sense resistor and a
constant current through the switch.
If no 3.3V input supply is available, short the 3.3V
SENSE
pin
to the 5V
IN
pin.
UU
U
PI FU CTIO S
