Datasheet
SLUS384B – NOVEMBER 1999 – REVISED JUNE 2000
4
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pin descriptions
CT: A capacitor connected to this pin sets the maximum fault time. The maximum time must be greater than
the time to charge external load capacitance. The nominal fault time is defined as:
T
FAULT
+ 22.2 10
3
C
T
Once the fault time is reached the output shuts down for a time given by:
T
SD
+ 0.667 10
6
C
T
This equates to a 3% duty cycle. The recommended minimum value for the C
T
capacitor is 0.1 µF.
FAULT: Open-drain output, which pulls low on any condition that causes the output to open; Fault, Thermal
Shutdown, Shutdown, and maximum sourcing current greater than the fault time.
GND: This is the most negative voltage in the circuit. All 4 ground pins should be used, and properly heat sunk
on the PCB.
IFAULT: A resistor connected from this pin to ground sets the fault threshold. The resistor versus fault current
is set by the formula
R
FAULT
+
105 kW
I
TRIP
IMAX: A resistor connected from this pin to ground sets the maximum sourcing current. The resistor vs the
output sourcing current is set by the formula:
R
IMAX
+
126 kW
Maximum Sourcing Current
SHTDWN: When this pin is brought low, the IC is put into sleep mode. The input threshold is hysteretic, allowing
the user to program a startup delay with an external RC circuit.
VIN: This is the input voltage to the UCC3918. The recommended operating voltage range is 3V to 6V. All VIN
pins should be connected together and to the power source.
VOUT: Output voltage for the circuit breaker. When switched the output voltage will be approximately:
V
OUT
+ V
IN
* 0.075W I
OUT
.
All VOUT pins should be connected together and to the load.
(1)
(2)
(3)
(4)
(5)