MAX6832–MAX6840
Ultra-Low-Voltage SC70 Voltage Detectors
and µP Reset Circuits
6
Maxim Integrated
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
signal whenever the V
CC
supply voltage falls below a
preset threshold (MAX6832–MAX6837) or RESET-IN
falls below the adjustable threshold (MAX6838/
MAX6839/MAX6840), keeping reset asserted for a fixed
timeout delay (Table 2) after V
CC
or RESET-IN has risen
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 20kΩ 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
RESET-IN threshold (V
RSTIN
). The low-leakage current
