Applications information – Rainbow Electronics MAX16024 User Manual

Page 13

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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

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