Datasheet

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SLUS247F − APRIL 1997 − REVISED NOVEMBER 2007
4
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APPLICATION INFORMATION
The UCCx946 supervisory circuit provides accurate reset and watchdog functions for a variety of
microprocessor applications. The reset circuit prevents the microprocessor from executing code during
undervoltage conditions, typically during power-up and power-down. In order to prevent erratic operation in the
presence of noise, voltage glitches where voltage amplitude and time duration are less than the values specified
in Figure 1 are ignored.
100
40
0
110 120 130 140 150 160 170 180
20
100
60
80
120
180
140
160
200
Figure 1.
OVERDRIVE VOLTAGE WITH RESPECT TO
RESET THRESHOLD
vs
DELAY TO OUTPUT LOW ON R
ESB
V
TH
− Overdrive Voltage − mV
T
DELAY
− Delay Time − µs
R
T
Senses Glitch,
RES
Goes Low for Reset Period
Glitches
Ignored,
RESB
Remains
High
The watchdog circuit monitors the microprocessor’s activity, if the microprocessor does not toggle WDI during
the programmable watchdog period WDO
goes low, alerting the microprocessor’s interrupt of a fault. The WDO
pin is typically connected to the non-maskable input of the microprocessor so that an error recovery routine can
be executed.