Datasheet

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UCD90124A

SLVSAN8 –JANUARY 2012

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Figure 30. Timing of GPIOs Configured for Watchdog Timer Operation

DATA AND ERROR LOGGING TO FLASH MEMORY

The UCD90124A 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 UCD90124A internal run-time clock via a PMBus host. For

example, a host processor with a real-time clock could periodically update the UCD90124A run-time clock to a

value that corresponds to the actual date and time. The host must translate the UCD90124A 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.

BROWNOUT FUNCTION

The UCD90124A can be enabled to turn off all nonvolatile logging until a brownout event is detected. A brownout

event occurs if V

drops below 2.9 V. In order to enable this feature, the user must provide enough local

capacitance to deliver up to 80 mA (consider additional load based on GPOs sourcing external circuits such as

LEDs) on for 5 ms while maintaining a minimum of 2.6 V at the device. If using the brownout circuit (Figure 31),

then a schottky diode should be placed so that it blocks the other circuits that are also powered from the 3.3V

supply.

With this feature enabled, the UCD90124A saves faults, peaks, and other log data to SRAM during normal

operation of the device. Once a brownout event is detected, all data is copied from SRAM to Flash. Use of this

feature allows the UCD90124A to keep track of a single run-time clock that spans device resets or system power

down (rather than resetting the run time clock after device reset). It can also improve the UCD90124A internal

response time to events, because Flash writes are disabled during normal system operation. This is an optional

feature and can be enabled using the MISC_CONFIG command. For more details, see the UCD90xxx

Sequencer and System Health Controller PMBus Command Reference.

Product Folder Link(s) :UCD90124A