LTC1391
APPLICATIONS INFORMATION
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 D
OUT
of one device
connected to the D
IN
of the next device, to be programmed
with a single data stream.
CLK
1
2
3
4
D
IN
D1
D2
D3
D4
D5
D
OUT
D1
D2
D3
D4
Figure 4. Digital Data Transfer Operation
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-1 multiplexer at the input to an LTC1400 A/D converter.
5V
0.1µF
0.1µF
OPTIONAL A/D
INPUT FILTER
–5V
0.1µF
CS
1
2
3
ANALOG
INPUTS
4
5
6
7
8
S0
S1
S2
S3
S4
S5
S6
S7
V
+
D
V
–
D
OUT
16
15
14
13
+
10µF
6
5
LTC1391
12
D
IN
A
11
CS
10
CLK
9
GND
1
2
3
ANALOG
INPUTS
4
5
6
7
8
S0
S1
S2
S3
S4
S5
S6
S7
V
+
D
V
–
16
15
14
13
D
OUT
LTC1391
12
D
IN
B
11
CS
10
CLK
9
GND
Figure 5. Daisy-Chaining Two LTC1391s for Expansion
sn1391 1391fas
+
U
W
U
U
D5
1391 • F04
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.
CLK
1
2
3
4
5
6
7
8
D
IN
ENA
A2
A1
A0
ENB
B2
B1
B0
1391 • F06
Figure 6. Data Sequence for MUX Expansion
5V
10µF
+
1
2
V
CC
A
IN
V
SS
8
7
10µF
CONV
LTC1400
3
V
REF
CLK
0.1µF 4
GND
D
OUT
– 5V
0.1µF
DATA
OUT
DATA IN
CS
CLK
1391 • F05
7
LINER [ LINEAR TECHNOLOGY ]
