Datasheet

LTC2978A
66
2978afa
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APPLICATIONS INFORMATION
continue to be held off, the appropriate bit is set in the
STATUS_MFR_SPECIFIC register, and the ALERTB pin
will be asserted low. When the output voltage has decayed
below its OFF threshold, the channel can enter the ON state.
Automatic Restart Via MFR_RESTART_DELAY
Command and CONTROLn pin
An automatic restart sequence can be initiated by driving
the CONTROL pin to the off state for >10μs then releasing
it. The automatic restart disables all V
OUT_EN
pins that are
mapped to a particular CONTROL pin for a time period
= MFR_RESTART_DELAY and then starts all DC-DC
Converters according to their respective TON_DELAYs.
(See Figure 17). V
OUT_ENn
pins are mapped to one of the
CONTROL pins by the MFR_CONFIG_LT C 2978 command.
This feature allows a host that is about to reset to restart
the power in a controlled manner after it has recovered.
responses to OV/UV faults. Fault responses can range from
disabling the DC/DC converter immediately, waiting to
see if the fault condition persists for some interval before
disabling the DC/DC converter, or allowing the DC/DC
converter to continue operating in spite of the fault
. If a DC/
DC
converter is disabled, the LTC2978A can be configured
to retry or latch-off. The retry interval is specified using
the MFR_RETRY_DELAY command. Latched faults are
reset by toggling the CONTROL pin, using the OPERATION
command, or removing and reapplying the bias voltage to
the V
IN_SNS
pin. All fault and warning conditions result in
the ALERTB pin being asserted low and the corresponding
bits being set in the status registers. The CLEAR_FAULTS
command resets the contents of the status registers and
deasserts the ALERTB output.
Output Overvoltage and Undervoltage Warnings
OV and UV warning threshold voltages are processed by
the LTC2978A’s ADC. These thresholds are set by the
VOUT_OV_WARN_LIMIT and VOUT_UV_WARN_LIMIT
commands respectively. If a warning occurs, the
corresponding bits are set in the status registers and
the ALERTB output is asserted low. Note that a warning
will never cause a V
OUT_EN
output pin to disable a DC/DC
converter.
Configuring the V
IN_EN
Output
The V
IN_EN
output may be used to disable the intermediate
bus voltage in the event of an output OV or UV fault.
Use the MFR_VINEN
_OV_FAULT
_RESPONSE and
MFR_VINEN_UV
_FAULT_RESPONSE registers to
configure the V
IN_EN
pin to assert low in response to
VOUT_OV/UV fault conditions. The V
IN_EN
output will stop
pulling low when the LTC2978A is commanded to re-enter
the ON state following a faulted-off condition.
Figure 17. Off Sequence with Automatic Restart
V
CONTROL
V
OUT_END
CONTROL
PIN BOUNCE
TOFF_DELAY0 TON_DELAY0
2978a F17
MFR_RESTART_DELAY
FAULT MANAGEMENT
Output Overvoltage and Undervoltage Faults
The high speed voltage supervisor OV and UV fault
thresholds are configured using the VOUT_OV_FAULT_
LIMIT and VOUT_UV_FAULT_LIMIT commands,
respectively. The VOUT_OV_FAULT_RESPONSE and
VOUT_UV_FAULT_RESPONSE commands determine the