CAT811
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6
DETAILED DESCRIPTION
Reset Timing
The reset signal is asserted LOW for the CAT811 when the power supply voltage falls below the threshold trip voltage and
remains asserted for at least 140 ms after the power supply voltage has risen above the threshold.
5 V
0 V
5 V
0 V
Threshold
Voltage
140 ms
minimum
Figure 6. Reset Timing Diagram
RESET
0 V
RESET
CAT811
CAT812
Reset
Timeout Period
V
CC
V
CC
V
CC
Transient Response
The CAT811 protect mPs against brownout failure. Short
duration transients of 4 ms or less and 100 mV amplitude
typically do not cause a false RESET.
Figure 7 shows the maximum pulse duration of
negative−going V
CC
transients that do not cause a reset
condition. As the amplitude of the transient goes further
below the threshold (increasing V
TH
− V
CC
), the maximum
pulse duration decreases. In this test, the V
CC
starts from an
initial voltage of 0.5 V above the threshold and drops below
it by the amplitude of the overdrive voltage (V
TH
− V
CC
).
Figure 7. Maximum Transient Duration without
Causing a Reset Pulse vs. Reset Comparator
Overdrive
RESET OVERDRIVE V
TH
− V
CC
(mV)
1000100101
0
5
10
15
20
25
30
TRANSIENT DURATION (ms)
CAT811Z
T
AMB
= 25°C
CAT811M
Valid Reset with V
CC
under 1.0 V
To ensure that the CAT811 RESET pin is in a known state
when V
CC
is under 1.0 V, a 100 kW pull−down resistor
between RESET
pin and GND is recommended; the value
is not critical.
Figure 8. RESET Valid with V
CC
Under 1.0 V
GND
100 kW
CAT811
Power
Supply
V
CC
RESETMR
