Datasheet

LTC2974
51
2974fc
For more information www.linear.com/LTC2974
pMbus coMManD DescripTion
TON_DELAY, TON_RISE, TON_MAX_FAULT_LIMIT and TOFF_DELAY
These commands share the same format and provide sequencing and timer fault and warning delays in ms.
TON_DELAY sets the amount of time in milliseconds that a channel waits following the start of an ON sequence before
its V
OUT_EN
pin enables a DC/DC converter. This delay is counted using SHARE_CLK only.
TON_RISE sets the amount of time in ms that elapses after the power supply has been enabled until the LTC2974’s
DAC soft-connects and servos the output voltage to the desired level if Mfr_dac_mode = 00b. This delay is counted
using SHARE_CLK only.
TON_MAX_FAULT_LIMIT is the maximum amount of time that the power supply being controlled by the LTC2974 can
attempt to power up the output without reaching the VOUT_UV_FAULT_LIMIT. If it does not, then a TON_MAX_FAULT
is declared. If the output reaches VOUT_UV_FAULT_LIMIT prior to TON_MAX_FAULT_LIMIT, the LTC2974 unmasks the
VOUT_UV_FAULT_LIMIT threshold. (Note that a value of zero means there is no limit to how long the power supply
can attempt to bring up its output voltage.) This delay is counted using SHARE_CLK only.
TOFF_DELAY is the amount of time that elapses after the CONTROL pin and/or OPERATION command is de-asserted
until the channel is disabled (soft-off). This delay is counted using SHARE_CLK if available, otherwise the internal
oscillator is used.
All of the above TON and TOFF delays are internally limited to 655ms, and rounded to the nearest 10µs. The read value
of these commands always returns what was last written and does not reflect internal limiting.
MFR_RESTART_DELAY
This command essentially sets the off time of a CONTROL pin initiated restart. If the CONTROL pin is toggled off for at
least 10µs then on, all dependent channels are disabled, held off for a time = Mfr_restart_delay, then sequenced back
on. CONTROL pin transitions whose OFF time exceeds Mfr_restart_delay are not affected by this command. A value
of all zeros disables this feature. This delay is counted using SHARE_CLK only.
This delay is internally limited to 13.1 seconds, and rounded to the nearest 200µs. The read value of this command
always returns what was last written and does not reflect internal limiting.
SEQUENCING TIMING LIMITS AND CLOCK SHARING
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED FORMAT UNITS EEPROM
DEFAULT
VALUE
REF
PAGE
TON_DELAY 0x60 Time from CONTROL pin and/or OPERATION
command = ON to V
OUT_EN
pin = ON.
R/W Word Y L11 ms Y 1.0
0xBA00
51
TON_RISE 0x61 Time from when the V
OUT_ENn
pin goes high
until the LTC2974 optionally soft-connects its
DAC and begins to servo the output voltage to
the desired value.
R/W Word Y L11 ms Y 10.0
0xD280
51
TON_MAX_FAULT_LIMIT 0x62 Maximum time from V
OUT_EN
pin on assertion
that an UV condition will be tolerated before a
TON_MAX_FAULT condition results.
R/W Word Y L11 ms Y 15.0
0xD3C0
51
TOFF_DELAY 0x64 Time from CONTROL pin and/or OPERATION
command = OFF to V
OUT_EN
pin = OFF.
R/W Word Y L11 ms Y 1.0
0xBA00
51
MFR_RESTART_DELAY 0xDC Delay from actual CONTROL active edge to
virtual CONTROL active edge.
R/W Word N L11 ms Y 400
0xFB20
51