Datasheet

LTC2974
33
2974fc
For more information www.linear.com/LTC2974
MFR_CONFIG_LTC2974 Data Contents
BIT(S) SYMBOL OPERATION
b[1] Mfr_config_dac_gain DAC buffer gain.
0: Select DAC buffer gain dac_gain_0 (1.38V full-scale)
1: Select DAC buffer gain dac_gain_1 (2.65V full-scale)
b[0] Mfr_config_ dac_pol DAC output polarity.
0: Encodes negative (inverting) DC/DC converter trim input.
1: Encodes positive (non-inverting) DC/DC converter trim input.
Cascade Sequence ON with Time-Based Sequence OFF
Cascade sequence ON allows a master power supply to sequence on a series of slave supplies by connecting each
power supply’s power good output to the control pin of the next power supply in the chain. Please note that the power
good signal is that of the power supply and not derived from the LTC2974’s internal power good processing. Power
good based cascade sequence OFF is not supported, OFF sequencing must be managed using immediate or time based
sequence OFF. See also “Tracking Based Sequencing”.
Cascade sequence ON is illustrated in Figure 15. For each slave channel Mfr_config_cascade_on is asserted high and
the associated control input is connected to the power good output of the previous power supply. In this configuration
each slave channel’s startup is delayed until the previous supply has powered up.
Cascade sequence OFF is not directly supported. Options for reversing the sequence when turning the supplies off
include:
• Using the OPERATION command to turn off all the channels with an appropriate off delay.
• Using the FAULT pin to bring all the channels down immediately or in sequence with an appropriate off delay.
When asserted, Mfr_config_cascade_on enables a slave channel to honor fault retries even when its control pin is
low. Additionally, if the system has faulted off after zero or a finite number of retries, an OPERATION command may
pMbus coMManD DescripTion
Figure 15. LTC2974 Configured to Cascade Sequence ON and Time-Base Sequence OFF
V
OUTP
RUN
V
OUTM
V
SENSEP0
V
SENSEM0
POWERGOOD0
FAULTB0FAULTB0
LTC2974
SLAVES
MASTER
CONTROL0
RECOMMENDED CONNECTION
WHEN HARDWARE ON/OFF
CONTROL IS REQUIRED
V
OUT_EN0
CONTROL1
CONTROL0
DC/DC LOAD
V
OUTP
RUN
V
OUTM
V
SENSEP1
V
SENSEM1
POWERGOOD1
V
OUT_EN1
CONTROL2
DC/DC LOAD
V
OUTP
RUN
V
OUTM
V
SENSEP2
V
SENSEM2
POWERGOOD2
V
OUT_EN2
CONTROL3
DC/DC LOAD
TO NEXT CONTROL PIN
V
OUTP
RUN
V
OUTM
V
SENSEP3
V
SENSEM3
POWERGOOD3
V
OUT_EN3
DC/DC LOAD
2974 F15