Datasheet

LTC4312
15
4312f
APPLICATIONS INFORMATIONAPPLICATIONS INFORMATION
Demultiplexer Function
Due to its bi-directional nature, the LTC4312 can be used
as a demultiplexer. This is shown in Figure 9 where two
channels are used to drive I
2
C data from the master side
with redundancy to the slave side. In this application the
SDAOUT/SCLOUT channels serve as the inputs while the
SDAIN/SCLIN channel is the output. Redundancy on the
master side provides protection against power supply
failure. In Figure 9, if the 5V bus supply on channel 1 falls
below 1.4V, channel 1 gets disabled as ENABLE1 is driven
below its digital threshold. Simultaneously, the V
BE
of the
NPN pull-down device on ENABLE2 falls below 0.7V and
it turns off. This causes ENABLE2 to be pulled up by R7
which in turn enables channel 2, causing control to be
transferred to the backup I
2
C master device.
Figure 9. The LTC4312 Confi gured as a 2:1 Demultiplexer in a System with Redundancy
LTC4312
GND
V
CC2
V
CC
4312 F09
SDAIN
SCLIN
ACC
DISCEN
FAULT
SDAOUT1
SCLOUT1
ENABLE1
SDAOUT2
SCLOUT2
ENABLE2
C1
0.01μF
SDA
SCL
FAULT
3.3V
R9
10k
R8
10k
R1
10k
R2
10k
5V
R3
10k
R4
10k
R5
100k
3.3V
R10
10k
R7
20k
R6
50k
PRIMARY
I
2
C
MASTER
CONTROLLER
CARD
BACKUP
I
2
C
MASTER
CONTROLLER
CARD
BF840