10.23.2 Resequence

The option to resequence is offered as a response to each type of fault. The resequence operation is not performed until the retries are exhausted for a given fault. During the resequence operation:

• All rails designated as Fault Shutdown Slaves (FSS) of the faulted rail are immediately disabled (Stop Immediately) or disabled according to the configured shutdown sequence (Stop With Delay)
• After the faulted rail and FSS rail enables are de-asserted and all of these rails have turned off (the voltage has fallen below POWER_GOOD_OFF), the UCD90xxx waits for a programmable delay time (for more information, see Section 10.42). While waiting for the rails to turn off, an error is reported if any of the rails reaches its TOFF_MAX_WARN_LIMIT. If this occurs, a configurable option is available to continue with the re-sequencing operation or not; for more information, see Section 10.42. It is also configurable to ignore rail’s POWR_GOOD_OFF and TOFF_WARNING status when resequencing. See Section 10.42. This is mainly for those rails whose EN signals are not controlled by UCD.
• Sequence n Times repeats until the faulted rail and FSS rails successfully achieve regulation or for a user-selected 1, 2, 3, or 4 times; for more information see Section 10.42. If the resequence operation is successful, this resequence counter is reset if all of the rails that where resequenced maintain normal operation (power-good and no retries) for 1 second. (If a rail is identified as one of the group of rails to resequence but the rail was not supposed to be on when the resequence occurs, the device does not wait for that rail to come on before declaring the resequence operation successful.) If the rails are resequenced the maximum number times and they fail to reach normal operation, a device reset is required to reset the resequence counter. Rails can be commanded off and then on in an attempt to get them back to normal operation.
• After the resequence delay time, the faulted rail and FSS rails are sequenced on according to the start-up sequence configuration; for more information see Section 10.42.

This resequence operation is straight-forward if there is only one set of faulted-rail and FSS rails. If two or more occur at the same time, you always get the more conservative behavior. For example, if a set of rails is already on its second resequence, and the device is configured to resequence three times, and another set of rails enters the resequence state, that second set of rails is only resequenced once. Another example – if one set of rails is waiting on all of its rails to shut down so that it can resequence, and another set of rails enters the resequence state, the device now waits for all rails from both sets to shut down before re-sequencing.

If the rails at the resequence state are set by the GPI fault response, the entire resequence action is suspended until the GPI fault is physically clear.