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7
LTC1391
sn1391 1391fas
APPLICATIONS INFORMATION
WU
U
Figure 6. Data Sequence for MUX Expansion
B2
B1
B0
CLK
CS
DIN
1391 F06
ENA
A2
A1
A0
ENB
12
34
56
78
To ensure that only one channel is switched on at any one
time, two sets of channel selection bits are needed for
DATA as shown in Figure 6. The first data sequence is used
to switch off one MUX and the second data sequence is
used to select one channel from the other MUX or
vice versa. In other words, if bit “ENA” is high and bit
“ENB” is low, one channel of MUX A is switched on and all
channels of MUX B are switched off. If bit “ENA” is low and
bit “ENB” is high, all channels at MUX A are switched off
and one channel of MUX B is switched on. Care should be
taken to ensure that only one LTC1391 is enabled at any
one time to prevent two channels from being enabled
simultaneously.
Multiplexer Expansion
Several LTC1391s can be daisy-chained to expand the
number of multiplexer inputs. No additional interface
ports are required for the expansion. Figure 5 shows two
LTC1391s connected at their analog outputs to form a
16-to-1multiplexerattheinputtoanLTC1400A/Dconverter.
D2
D1
D3
D4
D5
D2
D1
D3
D4
D5
CLK
DIN
DOUT
1391 F04
12
34
Figure 4. Digital Data Transfer Operation
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
S0
S1
S2
S3
S4
S5
S6
S7
V+
D
V –
DOUT
DIN
CS
CLK
GND
ANALOG
INPUTS
LTC1391
A
1
2
3
4
8
7
6
5
VSS
CONV
CLK
DOUT
VCC
AIN
VREF
GND
LTC1400
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
S0
S1
S2
S3
S4
S5
S6
S7
V+
D
V –
DOUT
DIN
CS
CLK
GND
LTC1391
B
5V
–5V
5V
DATA IN
CS
CLK
1391 F05
0.1
F
ANALOG
INPUTS
0.1
F
10
F
10
F
OPTIONAL A/D
INPUT FILTER
10
F
0.1
F
0.1
F
0.1
F
DATA
OUT
+
Figure 5. Daisy-Chaining Two LTC1391s for Expansion
bits clocked into the LTC1391 shift register before CS is
taken low select the MUX channel that is turned on. This
allows a series of devices, with the DOUT of one device
connected to the DIN of the next device, to be programmed
with a single data stream.