10-15

Dynamic Performance

The dynamic performance of the DAC, also depends on the

output amplifier selection. For low speed or static applica-

tions, AC specifications of the amplifier are not very critical.

For

high-speed

applications

slew-rate,

settling-time,

openloop gain and gain/phase-margin specifications of the

amplifier should be selected for the desired performance.

varies

between

10k

Similarly

the

output

capacitance

varies

between

the

minimum and the maximum values depending on the input

code. These variations necessitate the use of compensation

capacitors, when high speed amplifiers are used.

A capacitor in parallel with the feedback resistor (as shown

in Figure 10) provides the necessary phase compensation to

critically damp the output.

A small capacitor connected to the compensation pin of the

amplifier may be required for unstable situations causing

oscillations. Careful PC board layout, minimizing parasitic

capacitances, is also vital.

FIGURE 7. OUTPUT CAPACITANCE TEST CIRCUIT

FIGURE 8. FEEDTHROUGH ERROR TEST CIRCUIT

FIGURE 9. OUTPUT CURRENT SETTLING TIME TEST CIRCUIT

SCOPE

AD7541

17

16

18

1

2

3

17

5

4

BIT 1 (MSB)

BIT 12 (LSB)

+15V

NC

+15V

NC

1K

1MHz

HA2600

AD7541

17

16

18

1

2

3

15

5

4

+15V

3

2

6

GND

BIT 1 (MSB)

BIT 12 (LSB)

+15V

+10V

BIT 1 (MSB)

BIT 12 (LSB)

AD7541

EXTRAPOLATE

+100mV

100

Ω

GND

+5V

0V

DIGITAL INPUT

17

16

1

2

3

15

5

4

OSCILLOSCOPE

3t: 5% SETTLING

9t: 0.01% SETTLING

+15V

+10V

BIT 1 (MSB)

BIT 12 (LSB)

AD7541

GND

17

16

1

2

3

15

5

4

BIT 2

18

A

-

+

AD7541