6

LTC1391

Figure 6. Data Sequence for MUX Expansion

B2

B1

B0

CLK

CS

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

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

D

CS

CLK

GND

ANALOG

INPUTS

LTC1391

A

1

2

3

4

8

7

6

5

CONV

CLK

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

D

CS

CLK

GND

LTC1391

B

5V

–5V

–5V

5V

DATA IN

CS

CLK

1391 • F05

0.1

µF

ANALOG

INPUTS

0.1

µF

10

µF

10

µF

OPTIONAL A/D

INPUT FILTER

+

10

µF

+

0.1

µF

0.1

µF

0.1

µF

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

with a single data stream.