Data Sheet
ADP5042
Rev. A | Page 21 of 32
Watchdog 1 Input
The ADP5042 features a watchdog timer that monitors micro-
processor activity. A timer circuit is cleared with every low-to-
high or high-to-low logic transition on the watchdog input pin
(WDI1), which detects pulses as short as 80 ns. If the timer
counts through the preset watchdog timeout period (tWD1), reset
is asserted. The microprocessor is required to toggle the WDI1
pin to avoid being reset. Failure of the microprocessor to toggle
WDI1 within the timeout period, therefore, indicates a code
execution error, and the reset pulse generated restarts the
microprocessor in a known state.
As well as logic transitions on WDI1, the watchdog timer is also
cleared by a reset assertion due to an undervoltage condition on
the monitored rail. When reset is asserted, the watchdog timer
is cleared and does not begin counting again until reset deasserts.
Watchdog 1 timer can be disabled by leaving WDI1 floating or
by three-stating the WDI1 driver. The pin WMOD controls the
Watchdog 1 operating mode. If WMOD is set to logic level low,
Watchdog 1 is enabled as long as WDI1 is not in three-state. If
WMOD is set to logic level high, Watchdog 1 is always active
and cannot be disabled by a three-state condition. WMOD
input has an internal 200 k?pull-down resistor.
Watchdog 1 timeout is factory set to two possible values as
indicated in Table 18.
WDI1
nRSTO
t
RP1
t
RP1
t
WD1
SENSED
V
TH
1V
0V
0V
0V
Figure 58. Watchdog 1 Timing Diagram
Watchdog 2 Input
The ADP5042 features an additional watchdog timer that
monitors microprocessor activity in parallel to the first watchdog
with a much longer timeout. This provides additional security
and safety in case Watchdog 1 is incorrectly strobed. A timer
circuit is cleared with every low-to-high or high-to-low logic
transition on the watchdog input pin (WDI2), which detects pulses
as short as 8 祍. If the timer counts through the preset watchdog
timeout period (tWD2), reset is asserted, followed by a power
cycle of all regulators . The microprocessor is required to toggle
the WDI2 pin to avoid being reset and powered down. Failure
of the microprocessor to toggle WDI2 within the timeout period,
therefore, indicates a code execution error, and the reset output
nRSTO is forced low for tRP2. Then, all the regulators are turned
off for the tPOFF time. After the tPOFF period, the regulators are re-
activated according to a predefined sequence (see Table 9). Finally,
the reset line (nRSTO) is asserted for t
RP1
. This guarantees a
clean power-up of the system and proper reset.
As well as logic transitions on WDI2, the watchdog timer is also
cleared by a reset assertion due to an undervoltage condition on
the VTH monitored rail which can be factory programmable
between VOUT1, VOUT2, VOUT3, and AVIN (see Table 21).
When reset is asserted, the watchdog timer is cleared and does
not begin counting again until reset deasserts.
Watchdog 2 timeout is factory set to seven possible values as
indicated in Table 19. One additional option allows Watchdog 2
to be factory disabled.
VIN/VINx/ENx
VOUT1
VOUT2
VOUT3
nRSTO
WDI2
WSTAT
0V
0V
0V
0V
0V
t
POFF
t
RP2
t
WD2
t
RP1
t
RP1
t
WDCLEAR
t
D1
t
D1
t
D2
V
TH
t
D2
Figure 59. Watchdog 2 Timing Diagram (Assuming That VOUT2 Is the Monitored Rail)
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