SMP18

REV. C

–7–

APPLICATION TIPS

All unused digital inputs should be connected to logic LOW.

For analog inputs that may become temporarily disconnected, a

value ranging from 200 k

Ω to 1 MΩ.

Do not apply signals to the SMP18 with power off unless the in-

put current is limited to less than 10 mA.

TYPICAL APPLICATIONS

An 8-Channel Multiplexed D/A Converter

Figure 1 illustrates a typical demultiplexing function of the

SMP18. It is used to sample-and-hold eight different output

voltages corresponding to eight different digital codes from a

D/A converter. The SMP18’s droop rate of 40 mV/s requires a

refresh once every 250 ms before the voltage drifts beyond

1/2 LSB accuracy (1 LSB of an 8-bit DAC is equivalent to

19.5 mV out of a full-scale voltage of 5 V). For a 10-bit DAC

the refresh rate must be less than 60 ms, and for a 12-bit

system, 15 ms. This implementation is very cost effective com-

pared to using multiple DACs as the number of output channels

increases.

SMP18

13

14

15

12

1

2

4

5

3

16

6

7

8

9

10

11

+12V

3

15

1

5

16

17

4

+12V

+5V

REF02

+12V

GND

WR

CS

DAC8228

A

B

C

ADDRESS

DECODE

ADDRESS

BUS

DIGITAL

INPUTS

WR

DGND

INH

0.1µF

PIN 9

C

PIN 10

B

PIN 11

A

PIN 6

INH

CH

PIN

0

0

0

0

1

1

1

1

X

0

0

1

1

0

0

1

1

X

0

1

0

1

0

1

0

1

X

0

0

0

0

0

0

0

0

1

0

1

2

3

4

5

6

7

NONE

13

14

15

12

1

5

2

4

–

CHANNEL DECODING

Figure 1. 8-Channel Multiplexed D/A Converter