UCD9090
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SLVSA30A –APRIL 2011–REVISED AUGUST 2011
VOUT_OV_WARN – Flagged if a rail exceeds the specified OV warning limit at any time during startup or
operation
VOUT_OV_FAULT – Flagged if a rail exceeds the specified OV fault limit at any time during startup or operation
MAX_TOFF_WARN – Flagged if a rail that is commanded to shut down does not reach 12.5% of the nominal rail
voltage within the configured time
Faults are more serious than warnings. The PMBALERT# pin is always asserted immediately if a warning or fault
occurs. If a warning occurs, the following takes place:
Warning Actions
— Immediately assert the PMBALERT# pin
— Status bit is flagged
— Assert a GPIO pin (optional)
— Warnings are not logged to flash
A number of fault response options can be chosen from:
Fault Responses
— Continue Without Interruption: Flag the fault and take no action
— Shut Down Immediately: Shut down the faulted rail immediately and restart according to the rail
configuration
— Shut Down using TOFF_DELAY: If a fault occurs on a rail, exhaust whatever retries are
configured. If the rail does not come back, schedule the shutdown of this rail and all
fault-shutdown slaves. All selected rails, including the faulty rail, are sequenced off according to
their sequence-off dependencies and T_OFF_DELAY times. If Do Not Restart is selected, then
sequence off all selected rails when the fault is detected.
Restart
— Do Not Restart: Do not attempt to restart a faulted rail after it has been shut down.
— Restart Up To N Times: Attempt to restart a faulted rail up to 14 times after it has been shut down.
The time between restarts is measured between when the rail enable pin is deasserted (after any
glitch filtering and turn-off delay times, if configured to observe them) and then reasserted. It can
be set between 0 and 1275 ms in 5-ms increments.
— Restart Continuously: Same as Restart Up To N Times except that the device continues to restart
until the fault goes away, it is commanded off by the specified combination of PMBus
OPERATION command and PMBUS_CNTRL pin status, the device is reset, or power is removed
from the device.
— Shut Down Rails and Sequence On (Re-sequence): Shut down selected rails immediately or after
continue-operation time is reached and then sequence-on those rails using sequence-on
dependencies and T_ON_DELAY times.
SHUT DOWN ALL RAILS AND SEQUENCE ON (RESEQUENCE)
In response to a fault, or a RESEQUENCE command, the UCD9090 can be configured to turn off a set of rails
and then sequence them back on. To sequence all rails in the system, then all rails must be selected as
fault-shutdown slaves of the faulted rail. The rails designated as fault-shutdown slaves will do soft shutdowns
regardless of whether the faulted rail is set to stop immediately or stop with delay. Shut-down-all-rails and
sequence-on are not performed until retries are exhausted for a given fault.
While waiting for the rails to turn off, an error is reported if any of the rails reaches its TOFF_MAX_WARN_LIMIT.
There is a configurable option to continue with the resequencing operation if this occurs. After the faulted rail and
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