LTC2978
APPLICATIONS INFORMATION
•ꢀ DACꢀmanualꢀwithꢀhardꢀconnect.ꢀNonꢀservoꢀmode.ꢀTheꢀ
DAC hard connects to the feedback node at the value
in MFR_DAC. After connection, the DAC is moved by
writing DAC codes to the device.
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 >1±μs then releas-
ing it. The automatic restart disables all V
pins
OUT_EN
Margining
that are mapped to a particular CONTROL pin for a time
period=MFR_RESTART_DELAYandthenstartsallDC-DC
Converters according to their respective TON_DELAYs.
The LTC2978 margins and trims the output of a DC/DC
converter by driving current into or out of the feedback
node or the trim pin. Preset limits for margining are stored
in the VOUT_MARGIN_HIGH/LOW registers. Margining
is actuated by writing the appropriate bits to the OPERA-
TION register.
(see Figure 17). V
pins are mapped to one of the
OUT_ENn
CONTROLpinsbytheMFR_CONFIG_LTC2978command.
This feature allows a host that is about to reset to restart
the power in a controlled manner after it has recovered.
Margining requires the DAC to be connected. Margin
requests that occur when the DAC is disconnected will
force the DAC to soft connect. When in the margin high/
low state, the DAC cannot be disconnected. The DAC can
only be disconnected from the ON state.
CONTROL
PIN BOUNCE
V
CONTROL
V
OUT_END
2978 F17
Off Sequencing
TOFF_DELAY0
MFR_RESTART_DELAY TON_DELAY0
An off sequence is initiated using the CONTROL pin or
the OPERATION command. The TOFF_DELAY command
determines the amount of time that elapses from the be-
Figure 17. Off Sequence with Automatic Restart
ginning of the off sequence until each channel’s V
OUT_EN
pin is pulled low thus disabling its DC/DC converter.
FAULT MANAGEMENT
V
OUT
Off Threshold Voltage
Output Overvoltage and Undervoltage Faults
The MFR_VOUT_DISCHARGE_THRESHOLD command
register allows the user to specify the OFF threshold that
the output voltage must decay below before the channel
can enter/re-enter the ON state. The OFF threshold voltage
is specified by multiplying MFR_VOUT_DISCHARGE_
THRESHOLD and VOUT_COMMAND. In the event that an
output voltage has not decayed below its OFF threshold
before attempting to enter the ON state, the channel will
continue to be held off, the appropriate bit is set in the
STATUS_MFR_SPECIFICregister, andtheALERTBpinwill
be asserted low. When the output voltage has decayed
belowitsOFFthreshold,thechannelcanentertheONstate.
ThehighspeedvoltagesupervisorOVandUVfaultthresh-
oldsareconfiguredusingtheVOUT_OV_FAULT_LIMITand
VOUT_UV_FAULT_LIMIT commands, respectively. The
VOUT_OV_FAULT_RESPONSEandVOUT_UV_FAULT_RE-
SPONSE commands determine the 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 LTC2978 can be configured to
retry or latch-off. The retry interval is specified using the
2978fc
64
Linear Systems [ Linear Systems ]
