MAX16033 Datasheet, PDF (15/21 Pages) Maxim Integrated Products – Low-Power Battery Backup Circuits in Small μDFN Packages

Low-Power Battery Backup
Circuits in Small µDFN Packages
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 decreas-
es. 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 pro-
vides additional transient immunity.
3.0V OR 3.3V
V_CC
R1
R2
V-
MAX16033–
MAX16040
PFI
PFO
GND
PFO
V-
V_L VTRIP
0V
( ) ^VTRIP
=
⎡
R2_⎢ V_PFT +
⎣
V_PFH
⎛1
⎝⎜ R1
+
1⎞
R2 ⎠⎟
−
V_CC
R1
⎤
⎥
⎦
V_L
=
R2⎡⎢(VPFT)
⎣
⎛1
⎝⎜ R1
+
1⎞
R2 ⎠⎟
−
V_CC
R1
⎤
⎥
⎦
V_PFT = 1.235V
V_PFH = 12mV
Figure 9. Monitoring a Negative Voltage
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