LTC1645CS datasheet(6/24 Pages) LINER

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LTC1645

(14-Lead Package/8-Lead Package)

Whenever the timer is inactive, an internal N-channel FET

shorts the TIMER pin to ground. Activating the timer

connects a 2

µA current source from VCC1to the TIMER pin

and the voltage starts to ramp up with a slope dv/dt = 2

µA/

CTIMER. When the voltage reaches the trip point (1.23V),

the timer is reset by pulling the TIMER pin back to ground.

The timer period is (1.23V • CTIMER)/2µA.

GATE1 (Pin 12/Pin 6): Channel 1 High Side Gate Drive.

Connect to the gate of an external N-channel MOSFET. An

internal charge pump guarantees at least 4.5V of gate

drive. The charge pump is powered by the higher of VCC1

and VCC2. When the ON pin exceeds 0.8V, GATE1 is turned

on by connecting a 10

µA current source from the charge

pump output to the GATE1 pin and the voltage starts to

ramp up with a slope dv/dt = 10

µA/CGATE1. While the ON

pin is below 0.8V but above 0.4V, a 40

µA current source

pulls GATE1 toward ground. If the ON pin is below 0.4V,

the circuit breaker trips or the undervoltage lockout circuit

trips, the GATE1 pin is immediately pulled to ground with

a 12mA (typ) current source.

SENSE1 (Pin 13/Pin 7): VCC1 Circuit Breaker Set Pin. With

a sense resistor placed in the supply path between VCC1

and SENSE1, the circuit breaker trips when the voltage

across the resistor exceeds 50mV for more than 1.5

µs. If

the circuit breaker trip current is set to twice the normal

operating current, only 25mV is dropped across the sense

resistor during normal operation. To disable the circuit

breaker, short VCC1 and SENSE1 together.

VCC1 (Pin 14/Pin 8): Positive Supply Input. VCC1 can range

from 2.375V to 12V for normal operation. ICC1 is typically

1mA. An undervoltage lockout circuit disables the chip

whenever the voltage at VCC1 is less than 2.23V. All internal

logic is powered by VCC1.

–

2.23V

UVL

0.8V

0.4V

REF

1.5

µs

FILTER

1.12V

UVL

1.5

µs

FILTER

LOGIC

GLITCH

FILTER

REF

× CHARGE

PUMP

1.238V

REFERENCE

50mV

µA

–

VCC1

SENSE1

VCC2

SENSE2

GATE1

GATE2

RESET

GND

COMP+

COMPOUT

FAULT 4

1645 BD

TIMER 11

PI FU CTIO S

BLOCK DIAGRA

LTC1645CS Datasheet(PDF) 6 Page - Linear Technology

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