Detailed Description

Reset Output

A microprocessor’s (µP’s) reset input starts the µP in a

known state. The MAX6832–MAX6840 assert a reset to

prevent code-execution errors during power-up, power-

down, or brownout conditions. They also assert a reset

preset threshold (MAX6832–MAX6837) or RESET-IN

falls below the adjustable threshold (MAX6838/

MAX6839/MAX6840), keeping reset asserted for a fixed

above the reset threshold. The MAX6832/MAX6835/

MAX6838 use a push-pull active-low output, the

MAX6833/MAX6836/MAX6839 have a push-pull active-

high output, and the MAX6834/MAX6837/MAX6840

have an open-drain active-low output stage. Connect a

pullup resistor on the MAX6834/MAX6837/MAX6840’s

RESET output to any supply between 0 and 6V.

Manual Reset Input

Many µP-based systems require manual reset capabili-

ty, allowing the operator, a test technician, or external

logic circuitry to initiate a reset. Reset remains asserted

while MR is low, and for a fixed timeout delay after MR

returns high. This input has an internal 20k

Ω pullup

resistor, so it can be left open if it is not used. MR can

be driven with CMOS logic level, or with open-drain/col-

lector outputs. To create a manual reset function, con-

nect a normally open momentary switch from MR to

ground; external debounce circuitry is not required. If

MR is driven from long cables or if the device is used in

a noisy environment, connecting a 0.1µF capacitor from

MR to ground provides additional noise immunity.

RESET-IN Information

The MAX6838/MAX6839/MAX6840 feature a RESET-IN

input for monitoring supply voltages down to 0.44V. An

external resistive-divider network can be used to set

voltage monitoring thresholds as shown in Figure 1. As

the monitored voltage falls, the voltage at RESET-IN

decreases and asserts a reset when it falls below the

Ultra-Low-Voltage SC70 Voltage Detectors

and µP Reset Circuits

6

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MAX6838/

MAX6839/

MAX6840

RESET

TIMEOUT

PERIOD

RESET

OUTPUT

RESET-IN

RESET/

RESET

GND

MAX6832–

MAX6837

RESET

TIMEOUT

PERIOD

MANUAL

RESET

DETECT

RESET

OUTPUT

RESET/

RESET

GND

MR (MAX6835/MAX6836/MAX6837 ONLY)

MR

PULLUP

Functional Diagrams

R1

R2

RESET-IN

GND

RESET

(RESET)

( ) ARE FOR MAX6839

MAX6838/

MAX6839/

MAX6840

Figure 1. Setting the Adjustable Threshold Externally