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MAX6361 Datasheet(PDF) 6 Page - Maxim Integrated Products

Part No. MAX6361
Description  SOT23, Low-Power μP Supervisory Circuits with Battery Backup
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
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MAX6361 Datasheet(HTML) 6 Page - Maxim Integrated Products

   
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Backup-Battery Switchover
In a brownout or power failure, it may be necessary to
preserve the contents of the RAM. With a backup bat-
tery installed at BATT, the MAX6361/MAX6363/
MAX6364 automatically switch the RAM to backup
power when VCC falls. The MAX6363 has a BATT ON
output that goes high when in battery-backup mode.
These devices require two conditions before switching
to battery-backup mode:
1) VCC must be below the reset threshold.
2) VCC must be below VBATT. Table 2 lists the status
of the inputs and outputs in battery-backup mode.
The device will not power up if the only voltage
source is on BATT. OUT will only power up from
VCC at startup.
Manual Reset Input (MAX6361 only)
Many µP-based products require manual reset capabili-
ty, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. For the MAX6361, a logic
low on MR asserts reset. Reset remains asserted while
MR is low, and for a minimum of 150ms (tRP) after it
returns high. MR has an internal 20k
Ω pull-up resistor.
This input can be driven with TTL/CMOS logic levels or
with open-drain/collector outputs. Connect a normally
open momentary switch from MR to GND to create a
manual reset function; external debounce circuitry is not
required. If MR is driven from long cables or the device
is used in a noisy environment, connect a 0.1µF capaci-
tor from MR to GND to provide additional noise immunity.
Reset In (MAX6364 only)
RESET IN is compared to an internal 1.235V reference.
If the voltage at RESET IN is less than 1.235V, reset is
asserted. The RESET IN comparator may be used as
an undervoltage detector to signal a failing power sup-
ply. It can also be used as a secondary power-supply
reset monitor.
Reset Output
A µP’s reset input starts the µP in a known state. The
MAX6361/MAX6363/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 depend-
ing on the device chosen (see Ordering Information).
RESET or RESET asserts when VCC is below the reset
threshold and for at least 150ms (tRP) after VCC 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).
Applications Information
Operation Without a Backup
Power Source
The MAX6361/MAX6363/MAX6364 were designed for
battery-backed applications. If a backup battery is not
used, connect VCC 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 VCC
remains valid without danger of triggering a reset pulse.
The device does not enter battery-backup mode when
VCC stays above the reset threshold voltage.
Negative-Going VCC Transients
These supervisors are relatively immune to short-dura-
tion, negative-going VCC transients. Resetting the µP
when VCC 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 VCC
pulses, starting at VCC and ending below the reset
threshold by the magnitude indicated (reset threshold
overdrive). The graph shows the maximum pulse width
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
6
_______________________________________________________________________________________
PIN
STATUS
VCC
Disconnected from OUT
OUT
Connected to BATT
BATT
Connected to OUT. Current drawn from
the battery is less than 1µA (at VBATT =
2.8V, excluding IOUT) when VCC = 0.
RESET/RESET
Asserted
BATT ON
High state
MR, RESET IN
Inputs ignored
Table 2. Input and Output Status in
Battery-Backup Mode
SUFFIX
46
4.50
4.63
44
4.25
4.38
31
3.00
3.08
4.75
4.50
3.15
23
2.25
29
2.85
2.93
2.32
26
2.55
2.63
2.38
3.00
2.70
RESET THRESHOLD RANGES (V)
Table 1. Reset Threshold Ranges
MIN
MAX
TYP


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