LTM4677 datasheet(83/116 Pages) AD

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LTC3883/LTC3883-1

Rev. F

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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

0.0

0x8000

TOFF_FALL

0x65

Time from when the output starts to fall until the

output reaches zero volts.

R/W Word

L11

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

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 VOUT DAC. When the VOUT 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 VOUT 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

500

0xFBE8

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