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LTC1391C

8-Channel Analog Multiplexer with Cascadable Serial Interface

Linear Technology 

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 DOUT of one device

connected to the DIN of the next device, to be programmed

with a single data stream.

CLK

1

2

3

4

DIN

D1 D2 D3 D4 D5

DOUT

D1 D2 D3 D4 D5

1391 • F04

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.

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

CS

DIN

ENA A2 A1 A0 ENB B2 B1 B0

1391 • F06

Figure 6. Data Sequence for MUX Expansion

5V

0.1µF

ANALOG

INPUTS

1 S0

2 S1

3 S2

4 S3

5 S4

6 S5

7 S6

8 S7

V+ 16

D 15

V – 14

LTC1391DOUT

A

DIN

13

12

CS 11

CLK 10

GND 9

–5V

0.1µF

OPTIONAL A/D

INPUT FILTER

+

10µF

1 VCC

VSS 8

2 AIN

CONV 7

3

LTC1400

VREF

CLK

6

0.1µF 4

GND

DOUT 5

+

0.1µF

5V

10µF

+ 10µF

– 5V

0.1µF

DATA

OUT

ANALOG

INPUTS

1 S0

2 S1

3 S2

4 S3

5 S4

6 S5

7 S6

8

S7

V+ 16

D 15

V – 14

LTC1391DOUT

B

DIN

13

12

CS 11

CLK 10

GND 9

Figure 5. Daisy-Chaining Two LTC1391s for Expansion

DATA IN

CS

CLK

1391 • F05

6

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