LTC1422IN8 datasheet(5/16 Pages) LINER

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LTC1422

TYPICAL PERFORMANCE CHARACTERISTICS

PIN FUNCTIONS

TIMER (Pin 3): Analog system timing generator pin. This

pin is used to set the delay before the charge pump turns

on after the ON pin goes high. It also sets the delay before

the RESET pin goes high, after the output supply voltage

is good, as sensed by the FB pin.

When the timer is off, an internal N-channel shorts the

TIMER pin to ground. When the timer is turned on, a 2

µA

current from VCC is connected to the TIMER pin and the

voltage starts to ramp up with a slope given by: dV/dt =

µA/CTIMER. When the voltage reaches the trip point

(1.232V), the timer will be reset by pulling the TIMER pin

back to ground. The timer period is given by: (1.232V •

CTIMER )/2µA.

GND (Pin 4): Chip Ground.

FB (Pin 5): Analog comparator input used to monitor the

output supply voltage with an external resistive divider.

When the voltage on the FB pin is lower than the 1.232V,

the RESET pin will be pulled low. An internal filter helps

prevent negative voltage glitches from triggering a reset.

When the voltage on the FB pin rises above the trip point,

the RESET pin will go high after one timing cycle.

RESET (Pin 1) : Open drain output to GND with a 12

µA

pull-up to VCC. This pin is pulled low when the voltage at

the FB (Pin 5) goes below the FB pin threshold. The RESET

pin will go high one timing cycle after the voltage at the FB

pin goes above the FB pin threshold. An external pull-up

resistor can be used to speed up the rising edge on the

RESET pin or pull the pin to a voltage higher or lower than

VCC.

ON (Pin 2): Analog Input Pin. The threshold is set at 1.30V

with 80mV hysteresis. When the ON pin is pulled high, the

timer turns on for one cycle, then the charge pump turns

on. When the ON pin is pulled low longer than 40

µs, the

GATE pin will be pulled low and remain off until the ON pin

is pulled high.

If the ON pin is pulled low for less than 15

µs a soft reset

will occur. The charge pump remains on, and the RESET

pin is pulled low for one timing cycle starting 30

µs from

the falling edge of the ON pin.

The ON pin is also used to reset the electronic circuit

breaker. If the ON pin is cycled low and high following the

trip of the circuit breaker, the circuit breaker is reset and

a normal power-up sequence will occur.

RESET Voltage vs Temperature

TEMPERATURE (

°C)

–55

0.24

0.22

0.20

0.18

0.16

0.14

0.12

0.10

0.08

0.06

1422 G19

–35

–15

105

125

VCC = 5V

3mA PULL-UP

TEMPERATURE (

°C)

–55

1422 G20

–35

–15

105

125

VCC = 12V

VCC = 5V

VCC = 3V

ON Pin Pulse (Soft Reset) Time

vs Temperature

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