Datasheet

Monitoring a Negative Voltage
Connect the circuit, as shown in Figure 9, to use the
power-fail comparator to monitor a negative supply rail.
PFO stays low when V- is good. When V- rises to cause
PFI to be above +1.235V, PFO goes high. Ensure V
CC
comes up before the negative supply.
Negative-Going V
CC
Transients
The MAX16033–MAX16040 are relatively immune to
short-duration, negative-going V
CC
transients. Resetting
the μP when V
CC
experiences only small glitches is not
usually desired.
The Typical Operating Characteristics section contains
a Maximum Transient Duration vs. Reset Threshold
Overdrive graph. The graph shows the maximum pulse
width of a negative-going V
CC
transient that would not
trigger a reset pulse. As the amplitude of the transient
increases (i.e., goes further below the reset threshold
voltage), the maximum allowable pulse width decreases.
Typically, a V
CC
transient that goes 100mV below the reset
threshold and lasts for 25μs does not trigger a reset pulse.
A 0.1μF bypass capacitor mounted close to V
CC
provides
additional transient immunity.
Figure 9. Monitoring a Negative Voltage
GND
PFI
R2
R1
V-
MAX16033
MAX16040
3.0V OR 3.3V
V
CC
PFO
PFO
0V
V
L
V-
V
TRIP
( )
( )
CC
TRIP PFT PFH
CC
L PFT
PFT
PFH
11 V
V R2 V V
R1 R2 R1
11 V
V R2 V
R1 R2 R1
V 1.235V
V 12mV


= + +−






= +−




MAX16033–MAX16040 Low-Power Battery-Backup
Circuits in Small μDFN Packages
www.maximintegrated.com
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