7

®

DAC707/708/709

output. It is defined as a percent of FSR change in the output

per percent of change in either the positive supply (+V

negative supply (–V

nominal power supply voltages (see Figure 2). It is specified

for DC or low frequency changes. The typical performance

curve in Figure 2 shows the effect of high frequency changes

in power supply voltages.

Zero Adjustment

For unipolar (USB) configurations, apply the digital input

code that produces zero voltage or zero current output and

adjust the zero potentiometer for zero output.

For bipolar (BTC) configurations, apply the digital input

code that produces zero output voltage or current. See Table

II for corresponding codes and connection diagrams for zero

adjustments circuit connections. Zero calibration should be

made before gain calibration.

Gain Adjustment

Apply the digital input that gives the maximum positive

output voltage. Adjust the gain potentiometer for this posi-

tive full-scale voltage. See Table II for positive full-scale

voltages and the Connection Diagrams for gain adjustment

circuit connections.

FIGURE 2. Power Supply Rejection Versus Power Supply

Ripple Frequency.

OPERATING INSTRUCTIONS

POWER SUPPLY CONNECTIONS

For optimum performance and noise rejection, power supply

decoupling capacitors should be added as shown in the

Connection Diagram. 1

µF tantalum capacitors should be

located close to the D/A converter.

EXTERNAL ZERO AND GAIN ADJUSTMENT

Zero and gain may be trimmed by installing external zero

and gain potentiometers. Connect these potentiometers as

shown in the Connection Diagram and adjust as described

below. TCR of the potentiometers should be 100ppm/

°C or

less. The 3.9M

Ω and 270kΩ resistors (±20% carbon or

better) should be located close to the D/A converter to

prevent noise pickup. If it is not convenient to use these

high-value resistors, an equivalent “T” network, as shown in

Figure 3, may be substituted in place of the 3.9M

Ω resistor.

A 0.001

µF to 0.01µF ceramic capacitor should be connected

from GAIN ADJUST to ANALOG COMMON to prevent

noise pickup. Refer to Figures 4 and 5 for the relationship of

zero and gain adjustments to unipolar D/A converters.

FIGURE 3. Equivalent Resistances.

3.9M

Ω

180k

Ω

180k

Ω

10k

Ω

+ Full Scale

Input =

0000

1LSB

Range of

Zero

Adjust

Zero Adjust Translates the Line

Digital Input

Input = FFFF

Range of

Gain Adjust

Gain Adjust

Rotates the Line

H

H

FIGURE 4. Relationship of Zero and Gain Adjustments for

Unipolar D/A Converters, DAC708 and

DAC709.

FIGURE 5. Relationship of Zero and Gain Adjustments for

Bipolar D/A Converters, DAC707 and DAC708/

709

+ Full Scale

1LSB

Digital Input

Full Scale

Range

Gain Adjust

Rotates

the Line

– Full Scale

Input = 0000

Range of

Gain Adjust

H

Input = 7FFF

H

Input = 8000

H

Offset Adjust

Translates

the Line

Range and

Offset Adjust

Power Supply Ripple Frequency (Hz)

0.030

0.025

0.020

0.015

0.010

0.005

0

1

10

100

1k

10k

100k

+15V

Supply

+5V

Supply

–15V Supply