LTC1646
U W
TYPICAL PERFOR A CE CHARACTERISTICS
RESETOUT, PWRGD and FAULT
5V /3V
Discharge
OUT
OUT
Output Low Voltage vs I
Impedance vs Temperature
SINK
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
180
160
140
120
100
80
90°C
25°C
–45°C
60
40
20
0
0
1
2
3
4
5
–50
–25
0
25
50
75
100
I
(mA)
TEMPERATURE (°C)
SINK
1646 G22
1646 G23
U
U
U
PI FU CTIO S
RESETOUT (Pin 1): Open Drain Digital Output. Connect
the CPCI LOCAL_PCI_RST# signal to the RESETOUT pin.
RESETOUT is the logical combination of RESETIN and
PWRGD (see Table 4).
PWRGD (Pin 4) :Open Drain Power Good Digital Output.
Connect the CPCI HEALTHY# signal to the PWRGD pin.
PWRGD remains low while V3VOUT ≥ 2.9V and V5VOUT
≥
4.65V. When either of the supplies falls below its power
good threshold voltage, PWRGD will go high after a 50µs
deglitching time.
TIMER(Pin2):CurrentFaultInhibitTimingInput.Connect
a capacitor from TIMER to GND. With the chip turned off,
the TIMER pin is internally held at GND. When the chip is
turned on, a 5µA pull-up current source is connected to
TIMER. Current limit and voltage compliance faults will be
ignored until the voltage at the TIMER pin is greater than
1.25V.
5VOUT (Pin 5): 5V Output Sense. The PWRGD pin will not
pulllowuntilthe5VOUT pinvoltageexceeds4.65V. Ifno5V
input supply is available, tie the 5VOUT pin to the 3VOUT pin
in order to disable the 5VOUT power good function.
GND (Pin 6): Chip Ground
FAULT (Pin 3): Open Drain Digital I/O. FAULT is pulled low
when a current limit fault is detected. Faults are ignored
while the voltage at the TIMER pin is less than 1.25V. Once
the TIMER cycle is complete, FAULT will pull low and the
chip will latch off in the event of an overcurrent fault. The
chipwillremainlatchedintheoffstateuntiltheOFF/ONpin
is cycled high then low or the power is cycled.
3VOUT (Pin7):3.3VOutputSense.ThePWRGDpinwillnot
pull low until the 3VOUT pin voltage exceeds 2.90V. If no
3.3V input supply is available, tie the 3VOUT pin to the
5VOUT pin.
3VIN (Pin 8): 3.3V Supply Sense Input. An undervoltage
lockout circuit prevents the switches from turning on
whenthevoltageatthe3VIN pinislessthan2.5V.Ifno3.3V
input supply is available, connect a diode between 5VIN
and 3VIN (tie anode to 5VIN and cathode to 3VIN ). See
Figure 11.
Forcing the FAULT pin low with an external pull-down will
cause the chip to be latched into the off state after a 21µs
deglitching time.
1646fa
6
Linear [ Linear ]
