Manual Reset Outputs

6

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Detailed Description

Reset Output

The reset output is typically connected to the reset

input of a microprocessor (µP). A µP’s reset input starts

or restarts the µP in a known state. The MAX6453–

MAX6456 µP supervisory circuits provide the reset

logic to prevent code-execution errors during power-

up, power-down and brownout conditions (see the

Typical Operating Circuit).

RESET changes from high to low whenever the moni-

respective reset threshold voltages,

RESET remains low

for the reset timeout period, and then goes high.

RESET

changes from high to low after

MR input is held low for

the 3.36s (typ) setup period and deasserts 140ms (min)

after

MR deasserts.

RESET is guaranteed to be in the proper output logic

≥ 1V. For applications requiring valid

Valid

Manual Reset

The MAX6453/MAX6454 contain a manual reset output

(

MROUT) that asserts low immediately after driving MR

low and remains low for the reset timeout period after

MR goes high (Figure 1). The pushbutton manual reset

has no effect on the

RESET output. MROUT output can

be used to drive an NMI (nonmaskable interrupt) on the

processor to save valuable data.

The MAX6455/MAX6456’s

MROUT is asserted immedi-

ately upon driving

MR low. Driving MR low for longer

than the 3.36s (typ) setup period asserts

RESET. When

MR is deasserted, MROUT and RESET remain asserted

low for the reset timeout period after

MR goes high

(Figure 2).

Adjustable Input Voltage (RSTIN)

The MAX6453–MAX6456 monitor the voltage on RSTIN

using an adjustable reset threshold set with an external

resistor voltage divider (Figure 3). Use the following for-

mula to calculate the externally monitored voltage

Resistors R1 and R2 can have very high values to mini-

mize current consumption due to low leakage currents.

Set R2 to some conveniently high value (250k

Ω, for

example) and calculate R1 based on the desired reset

threshold voltage, using the following formula:

Ω

210ms

MROUT

RESET

MR

LONG SETUP PERIOD, 3.36s

Figure 2. MAX6455/MAX6456 Timing Diagram

210ms

MROUT

MR

Figure 1. MAX6453/MAX6454 Timing Diagram