MAX6361–MAX6364
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
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Operating Circuit,
the MAX6362 monitors two supply
voltages. To monitor the secondary 5V logic or analog
supply with a 4.60V nominal programmed reset thresh-
old, choose R2 = 100kΩ, and calculate R1 = 273kΩ.
Reset Output
A µP’s reset input starts the µP in a known state. The
MAX6361–MAX6364 µP supervisory circuits assert a
reset to prevent code-execution errors during power-
up, power-down, and brownout conditions. RESET is
guaranteed to be a logic low or high depending on the
device chosen (see
Ordering Information
). RESET or
RESET asserts when V
CC
is below the reset threshold
and for at least 150ms (t
RP
) after V
CC
rises above the
reset threshold. RESET or RESET also asserts when MR
is low (MAX6361) and when RESET IN is less than
1.235V (MAX6364). The MAX6362 watchdog function
will cause RESET (or RESET) to assert in pulses follow-
ing a watchdog timeout (Figure 1).
Applications Information
Operation Without a Backup
Power Source
The MAX6361–MAX6364 were designed for battery-
backed applications. If a backup battery is not used,
connect V
CC
to OUT and connect BATT to GND.
Replacing the Backup Battery
If BATT is decoupled with a 0.1µF capacitor to ground,
the backup power source can be removed while V
CC
remains valid without danger of triggering a reset pulse.
The device does not enter battery-backup mode when
V
CC
stays above the reset threshold voltage.
Negative-Going V
CC
Transients
These supervisors are relatively immune to short-dura-
tion, negative-going V
CC
transients. Resetting the µP
when V
CC
experiences only small glitches is usually
not desirable.
The
Typical Operating Characteristics
section shows a
graph of Maximum Transient Duration vs. Reset
Threshold Overdrive for which reset is not asserted.
The graph was produced using negative-going V
CC
pulses, starting at V
CC
and ending below the reset
threshold by the magnitude indicated (reset threshold
overdrive). The graph shows the maximum pulse width
that a negative-going V
CC
transient can typically have
without triggering a reset pulse. As the amplitude of the
transient increases (i.e., goes further below the reset
threshold), the maximum allowable pulse width
decreases. Typically, a V
CC
transient that goes 100mV
below the reset threshold and lasts for 30µs will not
trigger a reset pulse.
A 0.1µF bypass capacitor mounted close to the V
CC
pin provides additional transient immunity.
