Datasheet

LTC2978A
67
2978afa
For more information www.linear.com/LTC2978A
Figure 18. LTC2978A Application Circuit with Crowbar Protection on Intermediate Bus
V
PWR
V
IN_EN
V
IN_SNS
V
DACP0
V
SENSEP0
V
DACM0
V
SENSEM0
V
OUT_EN0
REFP
REFM
LTC2978A*
V
IN
<15V
GNDV
DD33
V
DD33
V
DD25
*SOME DETAILS OMITTED FOR CLARITY
ONLY ONE OF EIGHT CHANNELS SHOWN
V
IN
C
BYPASS
0.1µF
0.01µF
0.22µF
0.01µF
0.1µF
220Ω
MCR12DC2N2907
0.1µF 0.1µF
V
OUT
2978a
F18
RUN/SS
SGND
V
FB
GND
DC/DC
CONVERTER
LOAD
4.99k
BAT54
10k
100Ω
68Ω
V
CC
SENSE
R
SENSE
0.007Ω
Q1
Si4894BDY
LTC4210-3
TIMER GND
GATE
24.3k
10k
ON
APPLICATIONS INFORMATION
A charge-pumped 5µA pull-up to 12V is also available on the
V
IN_EN
output. Refer to the MFR_CONFIG_ALL_LTC2978
register description in the PMBus COMMAND DESCRIP-
TION section for more information.
Figure
18
shows an application circuit where the V
IN_EN
output is used to trigger a SCR crowbar on the intermediate
bus in order to protect the DC/DC converter’s load from a
catastrophic fault such as a stuck top gate.
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 LTC2978A. Each zone contains 4-channels. Figure 19
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.