Data Sheet

AD7228

Rev. D | Page 9 of 15

Interface Logic Information

The A0, A1, and A2 address lines select which DAC accepts

data from the input port. Table 6 shows the selection table for

the eight DACs and Figure 8 shows the input control logic.

When the WR signal is low, the input latch of the selected DAC

is transparent, and its output responds to activity on the data

bus. The data is latched into the addressed DAC latch on the

rising edge of WR. While WR is high, the analog outputs

remain at the value corresponding to the data held in their

respective latches.

Table 6. AD7228 Truth Table

Control Inputs

Operation

WR

A2

A1

A0

High

X

X

No operation, device

not selected

Low

Low

Low

Low

DAC 1 transparent

Low to High

Low

Low

Low

DAC 1 latched

Low

Low

Low

High

DAC 2 transparent

Low

Low

High

Low

DAC 3 transparent

Low

Low

High

High

DAC 4 transparent

Low

High

Low

Low

DAC 5 transparent

Low

High

Low

High

DAC 6 transparent

Low

High

High

Low

DAC 7 transparent

Low

High

High

High

DAC 8 transparent

A0

TO DAC 1 LATCH

A1

A2

WR

TO DAC 2 LATCH

TO DAC 3 LATCH

TO DAC 4 LATCH

TO DAC 5 LATCH

TO DAC 6 LATCH

TO DAC 7 LATCH

TO DAC 8 LATCH

1-OF-8

DECODER

Figure 8. Input Control Logic

Supply Current

range. Figure 9 shows a typical plot of power supply current vs.

temperature.

16

14

12

10

8

6

4

2

0

–2

–4

–6

–8

–10

–12

–60

–40

–20

0

20

40

TEMPERATURE (°C)

60

80

100

120

140

–14

Figure 9. Power Supply Current vs. Temperature

Applying the AD7228 Unipolar Output Operation

Unipolar output operation is the basic mode of operation for

each channel of the AD7228 and the output voltage has the same

ion are shown in Figure 10. The AD7228 can be operated from

single or dual supplies. The voltage at the reference input must

never be negative with respect to GND. Failure to observe this

precaution may cause parasitic transistor action and possible

device destruction. The code table for unipolar output operation

is shown in Table 7.

GND

LATCH 5

DAC 5

LATCH 6

DAC 6

LATCH 7

DAC 7

LATCH 8

CONTROL

LOGIC

DAC 8

8

WR

A1

A0

A2

AD7228

10

12

2

3

4

5

6

7

8

9

21

22

23

24

11

1

7

6

5

4

3

2

1

LATCH 1

DAC 1

LATCH 2

DAC 2

LATCH 3

DAC 3

LATCH 4

DAC 4

+12V TO +15V

DATA

BUS

MSB

LSB

0V OR –5V

13

20

Figure 10. Unipolar Output Circuit