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dc1978af
DEMO MANUAL DC1978A
COMMON DEMO BOARD OPERATIONS
CASCADE SEQUENCING
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 9. For each
slave channel Mfr_config_cascade_on bit is asserted
Figure 9. LTC2974 Configured to Cascade Sequence ON and Time Base Sequence OFF
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 im-
mediately or in sequence with an appropriate off delay.
V
OUTP
RUN
V
OUTM
V
SENSEP0
V
SENSEM0
POWERGOOD0
FAULTB0 FAULTB0
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
DC1978a F09