UCD9090
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SLVSA30A –APRIL 2011–REVISED AUGUST 2011
Turn-on Sequencing
The following sequence-on options are supported for each rail:
•
•
•
•
•
•
Monitor only – do not sequence-on
Fixed delay time (TON_DELAY) after an OPERATION command to turn on
Fixed delay time after assertion of the PMBUS_CNTRL pin
Fixed time after one or a group of parent rails achieves regulation (POWER_GOOD_ON)
Fixed time after a designated GPI has reached a user-specified state
Any combination of the previous options
The maximum TON_DELAY time is 3276 ms.
Turn-off Sequencing
The following sequence-off options are supported for each rail:
•
•
•
•
•
•
•
•
Monitor only – do not sequence-off
Fixed delay time (TOFF_DELAY) after an OPERATION command to turn off
Fixed delay time after deassertion of the PMBUS_CNTRL pin
Fixed time after one or a group of parent rails drop below regulation (POWER_GOOD_OFF)
Fixed delay time in response to an undervoltage, overvoltage, or max turn-on fault on the rail
Fixed delay time in response to a fault on a different rail when set as a fault shutdown slave to the faulted rail
Fixed delay time in response to a GPI reaching a user-specified state
Any combination of the previous options
The maximum TOFF_DELAY time is 3276 ms.
Rail 1 and Rail 2 are both sequenced “ON”
and “OFF” by the PMBUS_CNTRL pin
only
PMBUS_CNTRL PIN
TON_DELAY[1]
TOFF_DELAY[1]
Rail 2 has Rail 1 as an “ON” dependency
Rail 1 has Rail 2 as an “OFF” dependency
RAIL 1 EN
POWER_GOOD_ON[1]
POWER_GOOD_OFF[1]
RAIL 1 VOLTAGE
TON_DELAY[2]
TOFF_DELAY[2]
RAIL 2 EN
RAIL 2 VOLTAGE
TON_MAX_FAULT_LIMIT[2]
TOFF_MAX_WARN_LIMIT[2]
Figure 9. Sequence-on and Sequence-off Timing
Sequencing Configuration Options
In addition to the turn-on and turn-off sequencing options, the time between when a rail is enabled and when the
monitored rail voltage must reach its power-good-on setting can be configured using max turn-on
(TON_MAX_FAULT_LIMIT). Max turn-on can be set in 1-ms increments. A value of 0 ms means that there is no
limit and the device can try to turn on the output voltage indefinitely.
Rails can be configured to turn off immediately or to sequence-off according to rail and GPI dependencies, and
user-defined delay times. A sequenced shutdown is configured by selecting the appropriate rail and GPI
dependencies, and turn-off delay (TOFF_DELAY) times for each rail. The turn-off delay times begin when the
PMBUS_CNTRL pin is deasserted, when the PMBus OPERATION command is used to give a soft-stop
command, or when a fault occurs on a rail that has other rails set as fault-shutdown slaves.
Shutdowns on one rail can initiate shutdowns of other rails or controllers. In systems with multiple UCD9090s, it
is possible for each controller to be both a master and a slave to another controller.
Copyright © 2011, Texas Instruments Incorporated
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