5
LTC1422
1422fb
TYPICAL PERFORMANCE CHARACTERISTICS
UW
PIN FUNCTIONS
UUU
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 2µA
current from V
CC
is connected to the TIMER pin and the
voltage starts to ramp up with a slope given by: dV/dt =
2µA/C
TIMER
. 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 •
C
TIMER
)/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 12µA
pull-up to V
CC
. 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
V
CC
.
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 40µs, 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 15µs a soft reset
will occur. The charge pump remains on, and the RESET
pin is pulled low for one timing cycle starting 30µs 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
RESET VOLTAGE (V)
65
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
1422 G19
5–35
85
25–15
105
45
125
V
CC
= 5V
3mA PULL-UP
TEMPERATURE (°C)
–55
ON PIN PULSE TIME (µs)
65
55
50
45
40
35
30
25
20
15
10
1422 G20
5–35
85
25–15
105
45
125
V
CC
= 12V
V
CC
= 5V
V
CC
= 3V
ON Pin Pulse (Soft Reset) Time
vs Temperature
