4

LT1161

1161fa

Supply Pins: The two supply pins are internally connected

and must also be externally connected. In addition to

providing the operating current for the LT1161, the supply

pins also serve as the Kelvin connection for the current

sense comparators. The supply pins must be connected to

the positive side of the drain sense resistors for proper

operation of the current sense.

Input Pins: The input pins are active high and each pin

activates a separate internal charge pump when switched

ON. The input threshold is TTL/CMOS compatible but may

be taken as high as 15V with or without the supply

powered. Each input has approximately 200mV of hyster-

esis and an internal 75k pull-down resistor.

Gate Pins: The gate pins drive the power MOSFET gates.

When an input is ON, the corresponding gate pin is

pumped approximately 12V above the supply. These pins

have a relatively high impedance when above the rail (the

equivalent of a few hundred kilohms). Care should be

taken to minimize any loading by parasitic resistance to

ground or supply.

Sense Pins: Each sense pin connects to the input of a

supply-referenced comparator with a 65mV nominal off-

set. When a sense pin is taken more than 65mV below

supply, the MOSFET gate for that channel is driven low and

the corresponding timing capacitor discharged. Each cur-

rent-sense comparator operates completely independently.

The 65mV typical threshold has a +0.33%/

°C temperature

coefficient, which closely matches the TC of drain sense

resistors formed from copper PC traces.

Some loads require high in-rush currents. An RC time

delay can be added between the drain sense resistor and

the sense pin to ensure that the current-sense comparator

does not false trigger during start-up (see Applications

Information). However, a maximum of 10k

Ω can be in-

serted between a drain sense resistor and the sense pin. If

current sense is not required in any channel, the sense pin

for that channel is tied to supply.

ground sets the restart time following overcurrent detec-

recharged by a 14

µA nominal current source back to the

timer threshold, whereupon restart is attempted. If current

sense is not required in any channel, the timer pin for that

channel is left open.

Ground Pins: The two ground pins are internally con-

nected and must also be externally connected.

–

+

–

+

–

+

–

+

OSCILLATOR

AND

CHARGE PUMP

1.4V

75k

75k

1.4V

3V

TIMER

14

µA

INPUT

65mV

SENSE

GATE

1161 FD

(Each Channel)