CAT811RTBI Datasheet, PDF (6/9 Pages) ON Semiconductor – 4-Pin Microprocessor Power Supply Supervisors with Manual Reset

CAT811, CAT812
DETAILED DESCRIPTION
Reset Timing
The reset signal is asserted LOW for the CAT811 and HIGH for the CAT812 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.
5V
V_CC
Threshold
Voltage
0V
5V
CAT811 RESET
0V
V_CC
CAT812 RESET
0V
140 ms
minimum
Reset
Timeout Period
Figure 6. Reset Timing Diagram
V_CC Transient Response
The CAT811/812 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).
30
T_AMB = 25°C
25
20
CAT8xxZ
15
CAT8xxM
10
5
0
1
10
100
1000
RESET OVERDRIVE V_TH − V_CC (mV)
Figure 7. Maximum Transient Duration without
Causing a Reset Pulse vs. Reset Comparator
Overdrive
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. For the CAT812, a pull−up resistor from
RESET pin to V_CC is needed.
Power
Supply
V_CC
CAT811
MR RESET
GND
100 kW
Figure 8. RESET Valid with V_CC Under 1.0 V
Power
Supply
V_CC
CAT812
MR RESET
GND
100 kW
Figure 9. RESET Valid with V_CC Under 1.1 V
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