Rainbow Electronics MAX16068 User Manual
Page 21
______________________________________________________________________________________ 21
MAX16068
6-Channel, Flash-Configurable System Manager
with Nonvolatile Fault Registers
Watchdog Timer
The watchdog timer operates together with or indepen-
dently of the MAX16068. When operating in dependent
mode, the watchdog is not activated until RESET is
deasserted. When operating in independent mode,
the watchdog timer activates immediately after V
CC
exceeds the UVLO threshold and the boot phase is
complete. Set r73h[4] to ‘0’ to configure the watchdog
in dependent mode. Set r73h[4] to ‘1’ to configure the
watchdog in independent mode. See Table 16 for more
information on configuring the watchdog timer in depen-
dent or independent mode. The watchdog timer can be
reset by toggling the WDI inputs (GPIO4) or by writing a
‘1’ to r75h[5].
Dependent Watchdog Timer Operation
Use the watchdog timer to monitor FP activity in two
modes. Flexible timeout architecture provides an adjust-
able watchdog startup delay of up to 300s, allowing
complicated systems to complete lengthy boot-up rou-
tines. An adjustable watchdog timeout allows the super-
visor to provide quick alerts when the processor activity
fails. After each reset event (V
CC
drops below UVLO
then returns above UVLO, software reboot, manual reset
(MR), EN input going low then high, or watchdog reset),
the watchdog startup delay provides an extended time
for the system to power up and fully initialize all FP and
system components before assuming responsibility for
routine watchdog updates. Set r76h[6:4] to a value other
than ‘000’ to enable the watchdog startup delay. Set
r76h[6:4] to ‘000’ to disable the watchdog startup delay.
The normal watchdog timeout period, t
WDI
, begins after
the first transition on WDI before the conclusion of the
long startup watchdog period, t
WDI_STARTUP
(Figures 3
and 4). During the normal operating mode, WDO asserts
if the FP does not toggle WDI with a valid transition (high-
to-low or low-to-high) within the standard timeout period,
t
WDI
. WDO remains asserted until WDI is toggled or
RESET is asserted (Figure 4).
While EN is low, the watchdog timer is in reset. The
watchdog timer does not begin counting until the moni-
toring starts and RESET is deasserted. The watchdog
timer is reset and WDO deasserts any time RESET is
asserted (Figure 5). The watchdog timer is held in reset
while RESET is asserted.
Figure 3. Normal Watchdog Startup Sequence
Figure 4. Watchdog Timer Operation
LAST MON_
WDI
V
TH
t
WDI_STARTUP
< t
WDI
tRP
RESET
< t
WDI
WDI
WDO
0V
V
CC
0V
V
CC
< t
WDI
< t
WDI
< t
WDI
< t
WDI
> t
WDI
< t
WDI
< tWDI
t
WDI