Dual-Voltage µP Supervisory Circuits

with Sequenced Reset Outputs

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7

Applications Information

Selecting the Reset Timeout Capacitor

The RESET2 delay may be adjusted by the user with an

external capacitor connected from the CSRT pin to

ground. The MAX6391 includes a 600nA current source

voltage ramp is compared to the internal 1.25V refer-

ence to set the RESET2 delay period. The period is cal-

culated by:

where

∆V = 1.25V, I = 600nA, and C is the external

capacitor.

Simplifying,

A fixed internal 140ms (min) reset delay time for

RESET2 may be chosen by connecting the CSRT pin to

ramp and enables a separate fixed delay counter

chain. The MAX6391 internally determines the CSRT

connection and provides the proper timing setup.

can assert the RESET2 output but RESET IN2 will have

no effect on the RESET1 output.

An external resistive-divider network is required at

RESET IN2 for most applications. The divider resistors,

R3 and R4, may be calculated by the following formula:

set to a conveniently high value (500k

Ω for example, to

minimize current consumption) and the equation may

be solved for R3 by:

For single-supply operations requiring two reset out-

puts (RESET1 before RESET2), connect RESET IN2

Pullup Resistors

The MAX6391 includes open-drain outputs for both

RESET1 and RESET2. Two internal resistors, R1 and

R2, of 47k

Ω each are provided with internal connec-

tions to RESET1 and RESET2. These resistors may be

connected to the appropriate external voltage for inde-

requirements.

The MAX6392 includes a manual reset option, MR, that

replaces the R1 pullup resistor. The active-low manual

reset input forces both RESET1 and RESET2 low.

RESET2 is driven active before RESET1 in all cases

(10µs typ). The resets follow standard reset timing

specifications after the manual reset is released. The

47k

Ω resistor.

In addition to issuing a reset to the µP during power-up,

power-down, and brownout conditions, these devices

are relatively immune to short-duration, negative-going

Operating Characteristics show the Maximum Transient

Duration vs. Reset Comparator Overdrive graph. The

graph shows the maximum pulse width that a negative-

a reset signal. As the amplitude of the transient increas-

es, the maximum allowable pulse width decreases.

PART NUMBER

NOMINAL

THRESHOLD (V)

TOP MARK

MAX6391KA46

4.63

AAHJ

MAX6391KA44

4.38

AAHK

MAX6391KA31

3.08

AAHL

MAX6391KA29

2.93

AAHM

MAX6391KA26

2.63

AAHN

MAX6391KA23

2.32

AAHO

MAX6391KA22

2.19

AAHP

MAX6391KA17

1.67

AAHQ

MAX6391KA16

1.58

AAHR

MAX6392KA46

4.63

AAHS

MAX6392KA44

4.38

AAHT

MAX6392KA31

3.08

AAHU

MAX6392KA29

2.93

AAHV

MAX6392KA26

2.63

AAHW

MAX6392KA23

2.32

AAHX

MAX6392KA22

2.19

AAHY

MAX6392KA17

1.67

AAHZ

MAX6392KA16

1.58

AAIA

Selector Guide

Standard versions in bold face. Samples are typically available

for standard versions. Contact factory for availability.