Datasheet

LTC2974
38
2974fc
For more information www.linear.com/LTC2974
disabled when the slaves are tracking the master down to prevent false UC events. 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 20)
An important feature of
the LTC2974 is the ability to control, monitor and supervise DC/DC converters that are config
-
ured to track a master supply on and off.
The LTC2974 supports the following tracking features:
•
Track channels on and off without issuing false UV/UC events when the slave channels are tracking up or down.
• Track all channels down in response to a fault from a slave or master.
• Track all channels down when VIN_SNS drops below VIN_OFF, share clock is held low or Restore_user_all is issued.
• Ability to to reconfigure selected channels that are part of a tracking group to sequence up after the group has
tracked up or sequence down before the group has tracked down.
Tracking Implementation
The LTC2974 supports tracking through the coordinated programing of Ton_delay, Ton_rise,Toff_delay and Mfr_track_
en_chann. The master channel must be configured to turn on after all the slave channels have turned on and to turn
off before all the slave channels turn off. Slaves that are enabled before the master will remain off until the tracking pin
allows them to turn on. Slaves will be turned off via the tracking pin even though their run pin is still asserted. Ton_rise
must be extended on the slaves so that it ends relative to the rise of the TRACK pin and not the rise of the V
OUT_EN
pin.
When Mfr_track_en_chann is enabled the channel is reconfigured to:
• Sequence down on fault, VIN_OFF, SHARE_CLK low or RESTORE_USER_ALL.
• Ignore UV and UC during TOFF_DELAY. Note that ignoring UV and UC during TON_RISE and TON_MAX_FAULT
always happens regardless of how this bit is set.
pMbus coMManD DescripTion
Figure 20. Improperly Configured Fault Response on Faulting Channel Disrupts Tracking
V
OUT2
V
OUT3
VOUT_EN(3:2)
2974 F20
VOUT_EN1
VOUT_EN0
FAULTB0
CONTROL
UV FAULT ON CHANNEL 1 BRINGS DOWN MASTER
VIA FAULTB0. ALL SLAVES WITH ENABLED RUN
PINS TRACK DOWN CORRECTLY
SLAVE OUTPUT ENABLES TURN ON FIRST SLAVE OUTPUT ENABLES TURN OFF LAST
DISABLING VOUT_EN1
IMMEDIATELY IN RESPONSE
TO THE UV FAULT CAUSES
VOUT1 TO SHUT DOWN
OUT OF SEQUENCE
TON_RISE EXPIRES
FOR ALL CHANNELS.
UV AND UC DETECT ENABLED
ON ALL CHANNELS
TOFF_DELAY ENTERED
FOR ALL CHANNELS.
UV AND UC DETECT DISABLED
ON ALL CHANNELS
V
OUT1
V
OUT0