3

LTC1642

Circuit Breaker Trip Voltage

q

15

25

36

mV

q

45

52.5

60

mV

GATE Pin Output Current

q

–30

– 25

–20

µA

10

mA

External N-Channel Gate Drive

q

4.5

5.9

8.0

V

q

10

11.5

14

V

q

4.5

8.5

18

V

ON Pin Threshold (Low to High)

1.30

1.34

1.38

V

ON Pin Threshold (High to Low)

q

1.20

1.22

1.26

V

ON Pin Hysteresis

110

mV

Output Low Voltage

q

0.4

V

Logic Output Pull-Up Current

RESET, FAULT = GND

– 15

µA

Reference Output Voltage

No Load

q

1.208

1.220

1.232

V

Reference Line Regulation

2.97V

q

515

mV

Reference Load Regulation

q

2.5

7.5

mV

Reference Short-Circuit Current

4.5

mA

Comparator Offset Voltage

q

±10

mV

Comparator Hysteresis

3mV

DC ELECTRICAL CHARACTERISTICS

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

PI FU CTIO S

CRWBR (Pin 1): Combination Overvoltage Timer and

Crowbar Circuit Trigger. The timer sets the overvoltage

time needed to trigger the crowbar circuit. To use the timer

connect a capacitor C to ground; the trigger time is

9ms•C(

µF). When the timer is off an internal N-channel

pulls the pin to ground. The timer is started when the OV

comparator trips. A 45

µA current source is connected

a rate of 45/C(

µF) Volts/second. When the voltage reaches

410mV the current sourced by the pin increases to 1.5mA.

Boost this current with an NPN emitter follower to trigger

a crowbar SCR.

BRK TMR (Pin 2): Analog Timer which Limits the Time the

Part Remains In Current Limit. To use the timer connect a

capacitor from BRK TMR to ground. BRK TMR is pulled to

ground until the sense resistor current reaches its limit,

when the pin begins sourcing 20

µA and the pin voltage

increases at a rate of 20/C(

µF) Volts/second. When the pin

reaches 1.23V the GATE pin is pulled to ground and the

FAULT output is asserted until the chip is reset. To allow

the part to remain in current limit indefinitely ground BRK

TMR.

RST TMR (Pin 3): Analog System Timer. To use the timer

connect a capacitor from RST TMR to ground. This timer

sets the delay from the ON pin going high to the start of the

GATE pin’s ramp; it also sets the delay from output voltage

good, as sensed by the FB pin, to RESET going high. When

the timer is off, an internal N-channel shorts RST TMR to

ground. When the timer is turned on a 2

µA current from

ramp up at a rate of 2/C(

µF) Volts/second. The timer trips

when the voltage reaches 1.23V.