ltc2978 Linear Technology Corporation, ltc2978 Datasheet - Page 51

• Manufacturer Part Number: ltc2978
• Description: Octal Pmbus Power Supply Monitor And Controller With Eeprom
• Manufacturer: Linear Technology Corporation

ON State Operation
Once a channel has reached the ON state, the OPERATION
command can be used to command the DC/DC converter’s
output to margin high, margin low, or return to a nominal
output voltage indicated by VOUT_COMMAND. The user also
has the option of configuring a channel to continuously trim
the output of the DC/DC converter to the VOUT_COMMAND
voltage, or the channel’s V
high impedance state thus allowing the DC/DC converter
output voltage to go to its nominal value, V
the MFR_CONFIG command for details on how to configure
the output voltage servo.
Off Sequencing
An off sequence is initiated using the CONTROLn pin or
the OPERATION command. The TOFF_DELAY command
determines the amount of time that elapses from the be-
ginning of the off sequence until each channel’s V
pin is pulled low thus disabling its DC/DC converter.
V
The MFR_VOUT_DISCHARGE_THRESHOLD command
register allows the user to specify the OFF threshold that
the output voltage must decay below before the chan-
nel can enter/re-enter the ON state. The OFF threshold
voltage is specified by multiplying MFR_VOUT_DIS-
CHARGE_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_SPECIFIC register, and the
applicaTions inForMaTion
OUT
Off Threshold Voltage
DACPn
V
V
CONTROL
OUT_END
output can be placed in a
Figure 12. Off Sequence with Automatic Restart
TOFF_DELAY0
DCn ( NOM)
PIN BOUNCE
CONTROL
. Refer to
OUT_EN
MFR_RESTART_DELAY
ALERTB pin will be asserted low. When the output volt-
age has decayed below its OFF threshold, the channel can
enter the ON state.
Automatic Restart via MFR_RESTART_DELAY
Command
If the CONTROLn pin is toggled quickly (>10µs deglitch),
an automatic restart sequence can be triggered using the
MFR_RESTART_DELAY command for the channels enabled
by the CONTROLn pin (see Figure 12).
V
The high speed voltage supervisor OV and UV fault thresh-
olds are configured using the VOUT_OV_FAULT_LIMIT
and VOUT_UV_FAULT_LIMIT commands, respectively.
The VOUT_UV_FAULT_RESPONSE and VOUT_UV_FAULT_
RESPONSE commands determine the response to an
OV/UV fault. 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
MFR_RETRY_DELAY command. Latched faults are reset
by toggling the CONTROLn pin, using the OPERATION
command, or removing and reapplying the bias voltage
(V
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.
OUT
IN_SNS
OV/UV Faults
pin). All fault and warning conditions result in
TON_DELAY0
2978 F012
LTC2978

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