Datasheet

LTC2977
46
2977fa
For more information www.linear.com/LTC2977
MFR_CONFIG_LT C 2977 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 (noninverting) DC/DC converter trim input.
Tracking Supplies On and Off
The LTC2977 supports tracking power supplies that are equipped with a tracking pin and configured for tracking.
A tracking
power supply uses a secondary feedback terminal (TRACK) to allow its output voltage to be scaled to an
external
master voltage. Typically the external voltage is generated by the supply with the highest voltage in the sys-
tem, which
is fed to the slave track pins (see Figure 13a). Supplies that track a master supply must be enabled before
the
master supply comes up and disabled after the master supply comes down. Enabling the slave supplies when the
master is down requires supervisors monitoring the slaves to disable UV detection. All channels configured for track
-
ing must track off together in response to a fault on any channel or any other condition that can bring one or more of
the channels down. Prematurely disabling a slave channel via its RUN pin may cause that channel to shut down out
of sequence (see Figure 13d)
PMBus COMMAND DESCRIPTION
Figure 13a. LTC2977 Configured to Control, Supervise and Monitor Power Supplies Equipped with Tracking Pin
V
OUTP
RUN
V
OUTM
V
SENSEP0
V
SENSEM0
TRACK
FAULT00FAULTB0
LTC2977
CONTROL0
V
OUT_EN0
CONTROL0
DC/DC LOAD
V
OUTP
RUN
V
OUTM
V
SENSEP1
V
SENSEM1
TRACK
V
OUT_EN1
DC/DC LOAD
V
OUTP
RUN
V
OUTM
V
SENSEP2
V
SENSEM2
TRACK
V
OUT_EN2
DC/DC LOAD
V
OUTP
RUN
V
OUTM
V
SENSEP3
V
SENSEM3
TRACK
V
FB
V
DACP0
V
FB
V
DACP1
V
DACP3
V
FB
V
DACP2
V
FB
V
OUT_EN3
V
SENSEP0
V
SENSEP1
V
SENSEP2
V
SENSEM0
V
SENSEM1
V
SENSEM3
V
SENSEM2
V
SENSEP3
DC/DC LOAD
2977 F13a
R2_3
R1_3
R2_2
R1_2
R2_1
R1_1
PWRGD