Rainbow Electronics MAX16024 - Manual (Page 13)

Applications Information
The MAX16023/MAX16024 are protected for typical
short-circuit conditions of 10s or less. Shorting OUT to
ground for longer than 10s might damage the device.
Bypass V
CC and BATT to GND with a 0.1µF capacitor
each. Connect a 10µF low-ESR capacitor from OUT to
GND. All capacitors should be mounted as close as
possible to the device.
Monitoring an Additional Supply
The MAX16023 power-fail comparator can monitor
either positive or negative supplies using a resistive
divider to PFI (Figures 3 and 4). PFO can be used to
generate an interrupt to the µP or to trigger a reset. To
monitor a negative supply, connect the top of the resis-
tive divider to V
CC . Connect the bottom of the resistive
divider to the negative voltage to be monitored.
Adding Hysteresis to PFI
The power-fail comparators have a typical input hys-
teresis of V
PFT-HYS . This is sufficient for most applica-
tions where a power-supply line is being monitored
through an external voltage-divider (see the
Monitoring
an Additional Supply section). Figure 5 shows how to
add hysteresis to the power-fail comparator. Select the
ratio of R1 and R2 such that PFI sees V
PFT when V IN
falls to the desired trip point (V TRIP ). Resistor R3 adds
hysteresis. R3 is typically an order of magnitude greater
than R1 or R2. The current through R1 and R2 should
be at least 100µA to ensure that the 1µA (max) PFI
input current does not shift the trip point. R3 should be
larger than 50k
Ω to prevent it from loading down PFO.
Capacitor C1 adds additional noise rejection.
MAX16023/MAX16024
Battery-Backup Circuits with
Regulated Output Voltage
______________________________________________________________________________________ 13
MAX16023L
0.1 μF
GND
PFI
R2
R1
MR
PFO
ADDITIONAL SUPPLY RESET VOLTAGE
RESET
V 2
V
CC
V
1
RESET
μP
V
2(RESET)
= V
PFT
x
( ) R1 + R2
R2
Figure 3. Monitoring an Additional Supply by Connecting PFO
to MR
MAX16023
0.1 μF
GND
PFI
R2
R1
PFO
V
CC
V TRIP = V PFT -
(
5 - V PFT
) R2
R2
V TRIP IS NEGATIVE
V-
5V
PFO
0
+5V
V
TRIP V- 0
Figure 4. Monitoring a Negative Supply