The UCD9090A 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. Data and Error logging to flash memory can be disabled by user so that the data and error are only stored in the SRAM.

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 UCD9090A internal run-time clock via a PMBus host. For example, a host processor with a real-time clock could periodically update the UCD9090A run-time clock to a value that corresponds to the actual date and time. The host must translate the UCD9090A 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.