MAX16040PLA31+T Maxim Integrated Products, MAX16040PLA31+T Datasheet - Page 13

• Manufacturer Part Number: MAX16040PLA31+T
• Description: IC BATTERY BACKUP 3.08V 8-UDFN
• Manufacturer: Maxim Integrated Products
• Type: Battery Backup Circuitr

Specifications of MAX16040PLA31+T

• Number Of Voltages Monitored: 1
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: 140 ms Minimum
• Voltage - Threshold: 3.08V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-µDFN
• Undervoltage Threshold: 3 V
• Overvoltage Threshold: 3.15 V
• Manual Reset: Not Resettable
• Watchdog: No Watchdog
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 0 V
• Supply Current (typ): 22 uA
• Maximum Power Dissipation: 380.6 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

One way to help the watchdog timer to monitor 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 6
shows a flow diagram where the I/O driving the watch-
dog is set low in the beginning of the program, set high
at the beginning of every subroutine or loop, and set
low again when the program returns to the beginning. If
the program should hang in any subroutine, the watch-
dog would timeout and reset the µP.
Decouple BATT to GND with a 0.1µF capacitor. The
backup power source may be removed while V
remains valid without the danger of triggering a reset
pulse. The device does not enter battery-backup mode
when V
Monitor another voltage by connecting a resistive divider
to PFI as shown in Figure 7. The threshold voltage is:
where V
voltage will trip PFO.
To simplify the resistor selection, choose a value for R2
and calculate R1.
Figure 6. Watchdog Flow Diagram
CC
TH(PFI)
Watchdog Software Considerations
stays above the reset threshold voltage.
R1 = R2 [(V
V
Monitoring an Additional Power Supply
TH(PFI)
is the threshold at which the monitored
Replacing the Backup Battery
______________________________________________________________________________________
OR PROGRAM LOOP
= 1.235 (R1 / R2 + 1)
SUBROUTINE
WDI HIGH
RETURN
TH(PFI)
START
LOW
WDI
SET
END
SET
Power-Fail Comparator
/ 1.235) - 1]
Circuits in Small µDFN Packages
Low-Power Battery Backup
CC
Connect PFO to MR in applications that require RESET to
assert when the second voltage falls below its threshold.
RESET remains asserted as long as PFO holds MR low,
and for 140ms (min) after PFO goes high.
The power-fail comparator provides a typical hysteresis
of 12mV, which is sufficient for most applications where
a power-supply line is being monitored through an
external voltage-divider. Connect a voltage-divider
between PFI and PFO as shown in Figure 8a to provide
additional noise immunity. Select the ratio of R1 and R2
such that V
point, V
than 10 times the value of R1 or R2. The hysteresis win-
dow extends above (V
point, V
series with R3 as shown in Figure 8b causes the lower
trip point (V
teresis (V
margin without compromising the accuracy of the
power-fail threshold when the monitored voltage is
falling. Set the current through R1 and R2 to be at least
10µA to ensure that the 100nA (max) PFI input current
does not shift the trip point. Set R3 to be higher than
10kΩ to reduce the load at PFO. Capacitor C1 adds
additional noise rejection.
Figure 7. Monitoring an Additional Power Supply
Adding Hysteresis to the Power-Fail Comparator
TRIP
TRIP
TRIP
V
V+
CC
PFI
L
. R3 adds hysteresis and is typically more
. Connecting an ordinary signal diode in
) to coincide with the trip point without hys-
R1
R2
). This method provides additional noise
falls to 1.235V when V
V
PFI
CC
H
MAX16033–
MAX16040
) and below (V
GND
RESET
PFO
MR
IN
L
) the original trip
drops to its trip
TO µP
13