LTC2977 datasheet(107/138 Pages) AD

107 / 138 page

LTM4664A

107

Rev. 0

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PMBus COMMAND DETAILS

TON_MAX_FAULT_LIMIT

The TON_MAX_FAULT_LIMIT command sets the value, in milliseconds, on how long the unit can attempt to power

up the output without reaching the output undervoltage fault limit.

A data value of 0ms means that there is no limit and that the unit can attempt to bring up the output voltage indefinitely.

The maximum limit is 83 seconds.

This command has two data bytes and is formatted in Linear_5s_11s format.

VOUT_TRANSITION_RATE

When a PMBus device receives either a VOUT_COMMAND or OPERATION (Margin High, Margin Low) that causes the

output voltage to change this command set the rate in V/ms at which the output voltage changes. The commanded

rate of change does not apply when the unit is commanded on or off. The maximum allowed slope is 4V/ms.

This command has two data bytes and is formatted in Linear_5s_11s format.

Timing—Off Sequence/Ramp

COMMAND NAME

CMD CODE DESCRIPTION

TYPE

PAGED

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

0xC300

TOFF_MAX_WARN_LIMIT

0x66

Maximum allowed time, after TOFF_FALL

completed, for the unit to decay below

12.5%.

R/W Word

L11

0x8000

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 resulting turn off delay will have a typical delay of

270µs for TOFF_DELAY = 0 and an uncertainty of ±50µs for all values of TOFF_DELAY. TOFF_DELAY is not applied

when a fault event occurs

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 voltage

is commanded to zero. It is the ramp time of the VOUT DAC. When the VOUT DAC is zero, the PWM output will be set

to high impedance 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.

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