Datasheet

LTC2977
48
2977fa
For more information www.linear.com/LTC2977
Tracking Implementation
The LTC2977 supports tracking through the coordinated programing of Ton_delay, Ton_rise,Toff_delay and Mfr_config_
chan_mode. 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_config_chan_mode = 1Xb the channel is reconfigured to:
• Sequence down on fault, VIN_OFF, SHARE_CLK low or RESTORE_USER_ALL.
• Ignore UV during TOFF_DELAY. Note that ignoring UV during TON_RISE and TON_MAX_FAULT always happens
regardless of how these configuration bits are set.
The following example illustrates configuring an LTC2977 with one master channel and three slaves.
Master channel 0
TON_DELAY = Ton_delay_master
TON_RISE = Ton_rise_master
TOFF_DELAY = Toff_delay_master
Mfr
_config_chan_mode = 00
Slave channel
n
TON_DELAY = Ton_delay_slave
TON_RISE = Ton_delay_master + Ton_rise_slave
PMBus COMMAND DESCRIPTION
Figure 13d. Improperly Configured Fault Response on Faulting Channel Disrupts Tracking
V
OUT2
V
OUT3
VOUT_EN(3:2)
2977 F13d
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 DETECT ENABLED
ON ALL CHANNELS
TOFF_DELAY ENTERED
FOR ALL CHANNELS.
UV DETECT DISABLED
ON ALL CHANNELS
V
OUT1
V
OUT0