AD8522

input register and transferring the 12 bits of data into the de-

coded address determined by the address bits A and B in the se-

rial input register.

Unipolar Output Operation

This is the basic mode of operation for the AD8522. The

AD8522 has been designed to drive loads as low as 820

Ω in

parallel with 500 pF. The code table for this operation is shown

in Table III.

Table III. Unipolar Code Table

Hexadecimal

Decimal

Analog

Number in

Number in

Output

DAC Register

DAC Register

Voltage (V)

FFF

4095

+4.095

801

2049

+2.049

800

2048

+2.048

7FF

2047

+2.047

000

0

0

5

2

0

1

3

4

10

100

100k

10k

1k

LOAD RESISTANCE –

Ω

Figure 6. Output Swing vs. Load

80

60

40

20

0

–20

–40

–60

–80

123

OUTPUT VOLTAGE – Volts

POSITIVE

CURRENT

LIMIT

NEGATIVE

CURRENT

LIMIT

5.2

5.0

4.8

4.6

4.4

4.2

4.0

0.01

0.1

100

10

1.0

OUTPUT LOAD CURRENT – mA

PROPER OPERATION

VOLTAGE IS ABOVE

CURVE

Figure 7. Minimum Supply Voltage

vs. Load Current

100

90

10

0%

100µs/DIV

NBW = 1MHz

Figure 10. Broadband Noise

1

10

1000

100

100

1

0.1

10

0.01

+85

°C

–55

°C

+25

°C

OUTPUT SINK CURRENT – µA

Figure 8. Pull-Down Voltage vs. Out-

put Sink Current Capability

9

8

7

6

5

4

3

2

1

0

01

3

4

5

2

Figure 11. Supply Current vs. Logic

Input Voltage

Typical Performance Characteristics

is possible down to +4.3 V. The minimum operating supply

voltage versus load current plot, in Figure 7, provides informa-

TIMING AND CONTROL

The AD8522 has a 16-bit serial input register that accepts

clocked in data when the CS pin is active low. The DAC regis-

ters are updated by the Load Enable (LDA and LDB) pins.

The AD8522 offers two modes of data loading. The first mode,

hardware-load, directs the data currently clocked into the serial

shift register into either the DAC A or the DAC B register or

both depending on the external active low strobing of the LDA

or LDB pin. Serial data register bit Sf/Hd must be low for this

mode to be in effect.

The second mode of operation is software-load which is de-

signed to minimize the number of control lines connected to

the AD8522. In this mode of operation the LDA and LDB pins

act as one control input taking the present contents of the serial

–6–

REV. A