Datasheet

LTC3883/LTC3883-1
81
3883fa
For more information www.linear.com/LTC3883
PMBus COMMAND DETAILS
Timing—Off Sequence/Ramp
COMMAND NAME CMD CODE DESCRIPTION TYPE
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
TOFF_DELAY 0x64 Time from RUN and/or Operation off to the start
of TOFF_FALL ramp.
R/W Word L11 ms Y 0.0
0x8000
TOFF_F
ALL 0x65 Time from when the output starts to fall until the
output reaches zero volts.
R/W Word L11 ms Y 8.0
0xD200
TOFF_MAX_WARN_LIMIT
0x66 Maximum allowed time, after TOFF_FALL
completed, for the unit to decay below 12.5%.
R/W Word L11 ms Y 150
0xF258
TOFF_DELAY
The TOFF_DELAY command sets the time, in milliseconds, from when a stop condition is received until the output
voltage starts to fall. Values from 0 to 83 seconds are valid. The TON_DELAY will have a typical delay of 270µs with
an uncertainty of ±50µs.
This command is excluded from fault events.
This command has two data bytes and is formatted in Linear_5s_11s format.
TOFF_FALL
The TOFF_FALL command sets the time, in milliseconds, from the end of the turn-off delay time until the output volt
-
age is
commanded to zero. It is the ramp time of the V
OUT
DAC. When the V
OUT
DAC is zero, the part will three-state.
The part will maintain the mode of operation programmed. For defined TOFF_FALL times, the user should set the part
to
continuous conduction mode. Loading the max value indicates the part will ramp down at the slowest possible rate.
The minimum supported fall time is 0.25ms. A value less than 0.25ms will result in a 0.25ms ramp. The maximum
fall time is 1.3 seconds. The number of steps in TOFF_FALL is equal to TOFF_FALL (in ms)/0.1ms with an uncertainty
of ±0.1ms.
In discontinuous conduction mode, the controller will not draw current from the load and the fall time will be set by
the output capacitance and load current.
This command has two data bytes and is formatted in Linear_5s_11s format.
TOFF_MAX_WARN_LIMIT
The TOFF_MAX_WARN_LIMIT command sets the value, in milliseconds, on how long the unit can attempt to turn off
the output until a warning is asserted. The output is considered off when the V
OUT
voltage is less than 12.5% of the
programmed VOUT_COMMAND value. The calculation begins after TOFF_FALL is complete. TOFF_MAX_WARN_LIMIT
is not enabled if VOUT_DECAY is disabled.
A data value of 0ms means that there
is no limit and that the unit can attempt to turn off the output voltage indefinitely.
Other than 0, values from 120ms to 524 seconds are valid.
This command has two data bytes and is formatted in Linear_5s_11s format.
Precondition for Restart
COMMAND NAME CMD CODE DESCRIPTION TYPE
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_RESTART_ DELAY 0xDC Minimum time the RUN pin is held low by the
LTC3883.
R/W Word L11 ms Y 500
0xFBE8