LTC2978CUP View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2978CUP' PDF : 64 Pages View PDF
LTC2978
APPLICATIONS INFORMATION
• DAC manual with hard connect. Non servo mode. The
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.
Margining
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.
Margining requires the DAC to be connected. Margin
requests from a non-global OPERATION command that
occur when the DAC is disconnected will force the DAC
to soft connect. If a global (PAGE=0xFF) OPERATION
command is used to margin, the DACs must already be
connected using MFR_CONFIG_LTC2978 commands.
When in the margin high/low state, the DAC cannot be
disconnected. The DAC can only be disconnected from
the ON state.
Off Sequencing
An off sequence is initiated using the CONTROL pin or the
OPERATION command. The TOFF_DELAY value determines
the amount of time that elapses from the beginning of the
off sequence until each channel’s VOUT_EN pin is pulled
low, disabling its DC/DC converter.
VOUT Off Threshold Voltage
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_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 VOUT_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). VOUT_ENn pins are mapped to one of the
CONTROL pins by the MFR_CONFIG_LTC2978 command.
This feature allows a host that is about to reset to restart
the power in a controlled manner after it has recovered.
VCONTROL
CONTROL
PIN BOUNCE
VOUT_END
TOFF_DELAY0
2978 F17
MFR_RESTART_DELAY TON_DELAY0
Figure 17. Off Sequence with Automatic Restart
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
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
64
For more information www.linear.com/LTC2978
2978fd
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