MAX6368HKA31+T Maxim Integrated Products, MAX6368HKA31+T Datasheet - Page 10

• Manufacturer Part Number: MAX6368HKA31+T
• Description: IC SUPERVISOR MPU LP SOT23-8
• Manufacturer: Maxim Integrated Products
• Type: Battery Backup Circuitr

Specifications of MAX6368HKA31+T

• Number Of Voltages Monitored: 1
• Output: Open Drain or Open Collector
• Reset: Active High
• Reset Timeout: 150 ms Minimum
• Voltage - Threshold: 3.08V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
The watchdog monitors µP activity through the watch-
dog input (WDI). If the µP becomes inactive, reset
asserts. To use the watchdog function, connect WDI to
a bus line or µP I/O line. A change of state (high to low,
low to high, or a minimum 100ns pulse) resets the
watchdog timer. If WDI remains high or low for longer
than the watchdog timeout period (t
watchdog timer runs out and a reset pulse is triggered
for the reset timeout period (t
timer clears whenever reset asserts or whenever WDI
sees a rising or falling edge. If WDI remains in either a
high or low state, a reset pulse asserts periodically after
every t
BATT ON is a push-pull output that drives high when in
battery-backup mode. BATT ON typically sinks 3.2mA
at 0.1V saturation voltage. In battery-backup mode, this
terminal sources approximately 10µA from OUT. Use
BATT ON to indicate battery-switchover status or to
supply base drive to an external pass transistor for
higher current applications (Figure 3).
RESET IN is compared to an internal 1.235V reference.
If the voltage at RESET IN is less than 1.235V, reset
asserts. Use the RESET IN comparator as an undervolt-
age detector to signal a failing power supply or as a
secondary power-supply reset monitor.
To program the reset threshold (V
power supply, use the following (see Typical Operating
Circuit):
where V
choose a value for R2 and calculate R1:
10
Figure 2. MAX6366 Watchdog Timeout Period and Reset Active Time
______________________________________________________________________________________
RESET IN Comparator (MAX6368 Only)
WD
REF
BATT ON Indicator (MAX6367 Only)
(Figure 2).
= 1.235V. To simplify the resistor selection,
Watchdog Input (MAX6366 Only)
V
RTH
= V
RESET
REF
WDI
(R1 / R2 + 1)
t
t
RP
WD
RP
= RESET TIMEOUT PERIOD
= WATCHDOG TIMEOUT PERIOD
). The internal watchdog
RTH
) of the secondary
WD
), the internal
t
WD
t
RP
t
WD
Since the input current at RESET IN is 25nA (max),
large values (up to 1MΩ) can be used for R2 with no
significant loss in accuracy. For example, in the Typical
Operating Circuit, the MAX6368 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.
A µP’s reset input starts the µP in a known state. The
MAX6365–MAX6368 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 logic high, depending
on the device chosen (see the Ordering Information).
RESET or RESET asserts when V
threshold and for at least 150ms (t
above the reset threshold. RESET or RESET also
asserts when MR is low (MAX6365) and when RESET IN
is less than 1.235V (MAX6368). The MAX6366 watch-
dog function will cause RESET (or RESET) to assert in
pulses following a watchdog timeout (Figure 2).
The MAX6365–MAX6368 provide battery-backup func-
tions. If a backup power source is not used, connect
BATT to GND and OUT to V
One way to help the watchdog timer monitor the soft-
ware execution more closely is to set and reset the
watchdog at different points in the program rather than
pulsing the watchdog input periodically. Figure 4
shows a flow diagram in which the I/O driving the
t
RP
Watchdog Software Considerations
R1 = R2 [(V
Applications Information
a Backup Power Source
RTH
CC
/ V
.
Operation Without
REF
CC
RP
) - 1]
is below the reset
Reset Output
) after V
CC
rises