LTC1696

7

1696fb

For more information www.linear.com/LTC1696

PIN FUNCTIONS

FB1(Pin1):FirstFeedbackInput.FB1monitorsandsenses

the first supply output voltage through an external resistor

divider. This voltage is then compared with an internal

reference voltage of 0.88V, which sets the threshold for

anovervoltagefaultdetection.Ifthesensevoltageexceeds

the threshold level, the output response time at the OUT

pin is dependent on the feedback overdrive above the

threshold level. The higher the feedback overdrive, the

faster will be the response time.

GND (Pin 2): Power Ground. Return path for all device

currents.

VCC(Pin3):PowerSupply.Thepinisconnectedseparately

from the power supply output that the chip is monitoring.

Its input range is from 2.7V to 27V. The quiescent current

is typically 100µA in standby mode when the device is

operating at 5V. The quiescent current increases to 170µA

when operating at 12V.

OUT (Pin 4): Output Current Limit Driver. Capable of deliv-

eringcontinuouscurrent,typically80mA,athighsupplies.

The output current decreases with lower supply voltage.

This pin directly drives the SCR crowbar at high supply

voltage. It can also provide gate drive for an N-channel

MOSFET or the base of an NPN transistor, which drives

the gate of an external SCR at low supply voltage. It is

normally in the inactive low state in the standby mode. In

the event of an overvoltage fault condition, the OUT pin is

latched into the active high state. The latched active high

state is reset by pulling the TIMER/RESET pin low through

an N-channel MOSFET switch or if the supply voltage at

voltage of 1.94V.

FB2 (Pin 5): Second Feedback Input. FB2 monitors and

senses the second supply output voltage through an

external resistor divider. This voltage is then compared

with an internal reference voltage of 0.88V, which sets the

threshold for an overvoltage fault detection. If the sense

voltage exceeds the threshold level, the output response

time at the OUT pin is dependent on the feedback over-

drive above the threshold level. The higher the feedback

overdrive, the faster will be the response time.

TIMER/RESET (Pin 6): Glitch Filter Timer Capacitor,

Reset and External Trigger Input. The external capacitor

connected to this pin programs the internal glitch filter

time delay. The internal current source used to charge the

timer capacitor is typically 10µA with feedback overdrive

of less than 20mV above the feedback trip threshold from

one feedback input. The current source increases to 12µA

when the feedback overdrive increases to more than

100mV. It further increases to 18µA if larger overdrive

occurs from both feedback inputs. The default glitch filter

time delay without an external timer capacitor is fixed by

an internal capacitor of 5pF with the internal reference

voltage of 1.185V. The delay reduces with increases in

first and second feedback input overdrive. This pin also

serves as a reset input to clear the internal latch during

an overvoltage fault condition. If pulled low, it resets the

active high state of the internal latch. The reset signal to

this pin should be an open drain type. This pin can also be

driven high externally to activate the OUT pin active high

if the FB1 and FB2 voltages remain below the feedback

trip threshold.