3
LTC1642
V
CB
Circuit Breaker Trip Voltage V
CB
= (V
CC
– V
SENSE
), V
FB
= GND ● 15 25 36 mV
V
CB
= (V
CC
– V
SENSE
), V
FB
= 1V ● 45 52.5 60 mV
I
CP
GATE Pin Output Current Charge Pump On, V
GATE
= GND ● –30 –25 –20 µA
Charge Pump Off, V
GATE
= 5V 10 mA
∆V
GATE
External N-Channel Gate Drive V
GATE
– V
CC,
V
CC
= 3V ● 4.5 5.9 8.0 V
V
GATE
– V
CC,
V
CC
= 5V ● 10 11.5 14 V
V
GATE
– V
CC,
V
CC
= 15V ● 4.5 8.5 18 V
V
ONHI
ON Pin Threshold (Low to High) 1.30 1.34 1.38 V
V
ONLO
ON Pin Threshold (High to Low) ● 1.20 1.22 1.26 V
V
ONHYST
ON Pin Hysteresis 110 mV
V
OL
Output Low Voltage RESET, FAULT, COMPOUT I
O
= 1.5mA ● 0.4 V
I
PU
Logic Output Pull-Up Current RESET, FAULT = GND –15 µA
V
REF
Reference Output Voltage No Load ● 1.208 1.220 1.232 V
∆V
LNR
Reference Line Regulation 2.97V ≤ V
CC
≤ 16.5V, No Load ● 515 mV
∆V
LDR
Reference Load Regulation I
O
= 0mA to –1mA, Sourcing Only ● 2.5 7.5 mV
I
RSC
Reference Short-Circuit Current V
REF
= 0V 4.5 mA
V
COS
Comparator Offset Voltage V
CM
= V
REF
● ±10 mV
V
CHYST
Comparator Hysteresis V
CM
= V
REF
3mV
DC ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
CC
= 5V unless otherwise specified.
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
UUU
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 45µA current source is connected
from V
CC
to the CRWBR pin, and the voltage increases at
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 20µA 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 2µA current from
V
CC
is connected and the RST TMR pin voltage starts to
ramp up at a rate of 2/C(µF) Volts/second. The timer trips
when the voltage reaches 1.23V.
