3
FN9186.3
January 3, 2006
Pinout
28 LEAD QFN
TOP VIEW
1
2
3
4
5
6
7
21
20
19
18
17
16
15
28    27    26    25    24    23    22
8
9    10    11    12    13    14
SNS2
VO2
SS2
GT2
FLT2
PG2
CT2
SNS1
VO1
SS1
GT1
FLT1
PG1
CT1
Pin Descriptions
PIN
NAME
FUNCTION
DESCRIPTION
1
SNS1
Current Sense Input
This pin is connected to the current sense resistor and control MOSFET Drain node. It provides
current sense signal to the internal comparator and amplifier in conjunction with VS1 pin.
2
VO1
Output Voltage 1
This pin is connected to the control MOSFET switch source, which connects to a load. Internally, this
voltage is used for SS control.
3
SS1
Soft-Start Duration Set
Input
A capacitor from this pin to ground sets the output soft-start ramp slope. This capacitor is charged by
the internal 10礎 current source setting the soft-start ramp. The output voltage ramp tracks the SS
ramp by controlled enhancement of FET gate. Once ramp-up is completed, the capacitor continues
to charge to the CPVDD voltage rail. If common capacitor is used (by tying SS1, SS2 together and
the capacitor to GND from the connection) then both the outputs track each other as they ramp up.
4
GT1
Gate Drive Output
Direct connection to the gate of the external N-Channel MOSFET. At turn-on the Gate will charge to
4 X Vbias or 10V(max) from the 24礎 source.
5
FLT1
Fault Output
This is an open drain output. It asserts (pulls low) once the current regulation duration (determined
by the CTx timeout cap) has expired. This output is valid for Vbias>1V.
6
PG1
Power Good Output
This is an active low, open drain output. When asserted (logic zero), it indicates that the voltage on
UV1 pin is more than 643mV (633mV + 10mV hysteresis). This output is valid at VBIAS >1V.
7
CT1
Timer Capacitor
A capacitor from this pin to ground controls the current regulation duration from the onset of current
regulation to channel shutdown (current limit time-out). Once the voltage on CTx cap reaches
V
CT_Vth
the GATE output is pulled down and the FLT
is asserted.
The duration of current limit time-out = (C
TIM
*1.178)/10礎
When the OC comparator trips AND the RTR
/LTCH pin is pulled low, the ICs faulty channel remains
shut down for 64 cycles (each cycle length is equal to the current limit time-out duration).
8
RTR
/
LTCH
Retry Or Latch Input
This input dictates the IC behavior (for either channel) under OC condition. If it is pulled high (or left
floating), the IC will shut down upon OC time-out. If it is pulled low, the IC will go into retry mode after
an interval determined by the capacitor on CTx pin. The faulting channel will remain shut down for
64 cycles and will try to come out of it on the 65th cycle. Each cycle length is determined by the
formula shown in CT pin description.
9
GND
Chip Gnd
This pin is also internally shorted to the metal tab at the bottom of the IC.
10
PGND
Charge pump ground. Both GND and PGND must be tied together externally.
ISL6173