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LTC1232

sn1232 1232fas

active low for a minimum of 250ms from the moment the

push-button reset input is released from logic low level.

RST: RST is an Active High Logic Output. It is the inverse

of RST.

ST: Logic Input to Reset the Watchdog Timer. Driving ST

either high or low longer than the time-out period set by

the TD input, forces the reset outputs to active states for

a minimum of 250ms. The timer resets itself and begins to

time-out again with each high to low transition on the ST

input (see Figure 2).

PI FU CTIO S

APPLICATIO S I FOR ATIO

Figure 1. Reset Active Time

RST: Open Drain Logic Output for µP Reset Control.

The LTC1232 provides three ways to generate µP reset.

RST to remain active low for a minimum of 250ms.

Second, when the watchdog timer is not serviced prior to

a selected time-out period, the reset pulse generator also

forces RST to active low for a minimum of 250ms and

repeats for every time-out period. Third and the last, when

the PB RST pin stays active low for a minimum of 40ms,

RST becomes active low. The RST output will remain

The precision voltage comparator, C1, typically has 40mV

activate the reset outputs. Response time is typically 10µs.

pin should be bypassed with a 0.1µF capacitor with the

leads trimmed as short as possible.

Push-Button Reset

The LTC1232 provides a logic input pin, PB RST, for direct

connection to a push-button. This push-button reset input

requires an active low signal. Internally, this input signal is

debounced and timed for a minimum of 40ms. When this

Power Monitoring

The LTC1232 uses a bandgap voltage reference and a

precision voltage comparator, C1, to monitor the 5V

point. On power-up, the reset signals are held in active

reached to allow the power supply and microprocessor

to stabilize. On power-down, the RST signal remains

hold the microprocessor in stable shutdown condition.

Figure 1 shows the timing diagram of the RST signal.

V2

V2

V1

V1

V1 = VCC TRIP POINT

V2 = VCC TRIP POINT + VHYS

t1 = RESET ACTIVE TIME

t1

LTC1232 • TA03

RST

t1