LTC3882_15 Datasheet, PDF (81/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
PMBus COMMAND DETAILS (Output Timing, Delays and Ramping)
TON_MAX_FAULT_LIMIT
The TON_MAX_FAULT_LIMIT command sets the maximum time, in milliseconds, the unit is allowed from the beginning
of TON_RISE to power up the output without passing VOUT_UV_FAULT_LIMIT. A value of 0ms means there is no limit
and the unit can attempt to bring up the output voltage indefinitely. The maximum allowed TON_MAX is 8 seconds.
This command has two data bytes in Linear_5s_11s format.
VOUT_TRANSITION_RATE
The VOUT_TRANSITION_RATE command sets the rate at which the output voltage changes, in volts per millisecond
(or mV/µs), in response to a VOUT_COMMAND or OPERATION (margin) command. This rate of change does not ap-
ply to operations that fully turn the PWM channel on or off. Values from 1mV/ms to 4V/ms are considered valid. The
LTC3882 will not produce V_OUT transitions slower than 1mV/ms, and values exceeding 4V/ms cause the device to
transition the output as quickly as possible, limited only by PWM analog loop response.
This command has two data bytes in Linear_5s_11s format.
TOFF_DELAY
The TOFF_DELAY command sets the delay, in milliseconds, between a stop condition and the beginning of the output
voltage fall. Values from 0s to 16s are considered valid.
This command has two data bytes in Linear_5s_11s format.
TOFF_FALL
The TOFF_FALL command sets the time, in milliseconds, from the end of TOFF_DELAY until the output voltage is com-
manded fully to zero. The part attempts to linearly reduce the commanded output voltage to zero during TOFF_FALL.
At the end of this period, the PWM output is disabled.
The part will maintain its programmed PWM operating mode during TOFF_FALL. Using continuous conduction mode
will produce a well defined V_OUT ramp off but may result in negative output current. The minimum supported fall time
is 0.25ms, or any value that results in a rate of fall exceeding 4V/ms. Programmed values less than this will result in a
commanded 0.25ms ramp, possibly limited by PWM analog loop response. Maximum fall time is 1.3 seconds.
In discontinuous conduction mode, the controller will not be able to draw current from the load and fall time will be
set by output capacitance and load current.
This command has two data bytes in Linear_5s_11s format.
TOFF_MAX_WARN_LIMIT
The TOFF_MAX_WARN_LIMIT command sets the time, in milliseconds, the unit is allotted to have the output off after
TOFF_FALL completes before a warning is issued. The output is considered off when V_OUT is less than 12.5% of the
VOUT_COMMAND value.
A data value of 0ms means there is no limit and the unit can attempt to turn the output off indefinitely. There is also
no limit enforced if bit 0 of MFR_CHAN_CONFIG_LTC3882 is set.
This command has two data bytes in Linear_5s_11s format.
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