Datasheet

LTC2977
81
2977fa
For more information www.linear.com/LTC2977
APPLICATIONS INFORMATION
Multichannel Fault Management
Multichannel fault management is handled using the
bidirectional FAULTBzn pins. The “z” designates the fault
zone which is either 0 or 1. There are two fault zones in
the LTC2977. Each zone contains 4-channels. Figure 20
illustrates the connections between channels and the
FAULTBzn pins.
• The MFR_FAULTBz0_PROPAGATE command acts like a
programmable switch that allows faulted-off conditions
from a particular channel (PAGE) to propagate to
either FAULTBzn output in that channel’s zone. The
MFR_FAULTBzn_RESPONSE command controls similar
switches on the inputs to each channel that allow any
channel to shut down in response to any combination
of the FAULTBzn pins within a zone. Channels respond
-
ing to a FAULTBzn pin pulling low will attempt a new
start sequence when the FAULTBzn pin in question is
released by the faulted channel.
• To establish dependencies across fault zones, tie the
fault pins together, e.g., FAULTB01 to FAULTB10. Any
channel can depend on any other. To disable all channels
in response to any channel faulting off, short all the
FAULTBzn pins together, and set MFR_FAULTBzn_
PROPAGATE = 0x01 and MFR_FAULTBzn_RESPONSE
= 0x0F for all channels
.
• A FAULTBzn pin can also be asserted low by an external
driver in order to initiate an off-sequence after a 10µs
deglitch delay.
INTERCONNECT BETWEEN MULTIPLE LTC2977’S
Figure 21 shows how to interconnect the pins in a typical
multi-LTC2977 array.
• All V
IN_SNS
lines should be tied together in a star type
connection at the point where V
IN
is to be sensed.
This will minimize timing errors for the case where the
ON_OFF_CONFIG is configured to start the LTC2977
based on V
IN
and ignore the CONTROL line and the
OPERATION command. In multi-part applications that
are sensitive to timing differences, it is recommended
that the Vin_share_enable bit of the MFR_CONFIG_
ALL_LTC2977 register be set high in order to allow
SHARE_CLK to synchronize on/off sequencing in
response to the VIN_ON and VIN_OFF thresholds.
• Connecting all V
IN_EN
lines together will allow selected
faults on any DC/DC converter’s output in the array to
shut off a common input switch.
• ALERTB is typically one line in an array of PMBus con
-
verters. The LTC2977
allows a rich combination of faults
and warnings to be
propagated to the ALERTB pin.
Figure 21. Typical Connections Between Multiple LTC2977s
VIN_SNS
VIN_EN
SDA
SCL
ALERTB
CONTROL0
CONTROL1
WDI/RESETB
FAULTB00
FAULTB01
FAULTB10
FAULTB11
SHARE_CLK
PWRGD
GND
LTC2977 N-1
VIN_SNS
VIN_EN
SDA
SCL
ALERTB
CONTROL0
CONTROL1
WDI/RESETB
FAULTB00
FAULTB01
FAULTB10
FAULTB11
SHARE_CLK
PWRGD
GND
2977 F21
LTC2977 N
TO V
IN
OF
DC/DCs
TO INPUT
SWITCH
TO HOST CONTROLLER
TO OTHER LTC2977s–10k EQUIV PULL-UP RECOMMENDED
ON EACH LINE EXCEPT SHARE_CLK (USE 5.49k)