LTC1235

8

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APPLICATIONS INFORMATION

Power Monitoring

The LTC1235 uses a bandgap voltage reference and a

precision voltage comparator C1 to monitor the 5V supply

the reset voltage threshold, the reset outputs are forced

to active states. The reset voltage threshold accounts for

the reset signals are held active states for a minimum

of 140ms after the reset voltage threshold is reached to

allow the power supply and microprocessor to stabilize.

On power-down, the RESET signal remains active low

the microprocessor in stable shutdown condition. Figure

1 shows the timing diagram of the RESET signal.

The precision voltage comparator, C1, typically has 40mV

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

Figure 1. Reset Active Time

Figure 2. Push-Button Reset

pin should be bypassed with a 0.1μF capacitor with the

leads trimmed as short as possible.

LOW LINE is the output of the precision voltage compara-

LOW LINE goes low. LOW LINE returns high as soon as

Push-Button Reset

The LTC1235 provides an logic input pin for direct con-

nection to a push-button. The push-button reset input,

PB RST, requires an active low signal. Internally, this input

signal is debounced and timed for a minimum of 40ms.

When this condition is satisfied, the reset pulse generator

forces the reset outputs to active states. The reset signals

will remain in active states for a minimum of 140ms from

the moment the push-button reset input is released from

logic low level (Figure 2).

t1

t1 = RESET ACTIVE TIME

V1 = RESET VOLTAGE THRESHOLD

V2 = RESET VOLTAGE THRESHOLD +

RESET THRESHOLD HYSTERESIS

t1

V2

V2

V1

V1

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RESET

LOW LINE

LOGIC LOW

t1

LOGIC

HIGH

t2

LOGIC HIGH

LOGIC LOW

RESET

RESET

PB RST

t1 = PUSH-BUTTON RESET LOW TIME

t2 = RESET ACTIVE TIME

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