UCD9090
SLVSA30A –APRIL 2011–REVISED AUGUST 2011
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Table 8. WDT Initial Wait
Time (continued)
WDT INITIAL WAIT TIME
400 ms
800 ms
1.6 s
3.2 s
6.4 s
12.8 s
25.6 s
51.2 s
102 s
205 s
410 s
819 s
1638 s
The watchdog timeout is programmable from 0.001s to 32.256s. See the UCD90xxx Sequencer and System
Health Controller PMBus Command Reference for details on configuring the watchdog timeout. If the WDT times
out, the UCD9090 can assert a GPIO pin configured as WDO that is separate from a GPIO defined as
system-reset pin, or it can generate a system-reset pulse. After a timeout, the WDT is restarted by toggling the
WDI pin or by writing to SYSTEM_WATCHDOG_RESET over I2C.
<tWDI
<tWDI
<tWDI
tWDI
<tWDI
WDI
WDO
Figure 25. Timing of GPIOs Configured for Watchdog Timer Operation
DATA AND ERROR LOGGING TO FLASH MEMORY
The UCD9090 can log faults and the number of device resets to flash memory. Peak voltage measurements are
also stored for each rail. To reduce stress on the flash memory, a 30-second timer is started if a measured value
exceeds the previously logged value. Only the highest value from the 30-second interval is written from RAM to
flash.
Multiple faults can be stored in flash memory and can be accessed over PMBus to help debug power-supply
bugs or failures. Each logged fault includes:
•
•
•
•
Rail number
Fault type
Fault time since previous device reset
Last measured rail voltage
The total number of device resets is also stored to flash memory. The value can be reset using PMBus.
With the brownout function enabled, the run-time clock value, peak monitor values, and faults are only logged to
flash when a power-down is detected. The device run-time clock value is stored across resets or power cycles
unless the brownout function is disabled, in which case the run-time clock is returned to zero after each reset.
It is also possible to update and calibrate the UCD9090 internal run-time clock via a PMBus host. For example, a
host processor with a real-time clock could periodically update the UCD9090 run-time clock to a value that
corresponds to the actual date and time. The host must translate the UCD9090 timer value back into the
appropriate units, based on the usage scenario chosen. See the REAL_TIME_CLOCK command in the
UCD90xxx Sequencer and System Health Controller PMBus Command Reference for more details.
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