7

®

DAC701, 702, 703

POWER SUPPLY SENSITIVITY

Power supply sensitivity is a measure of the effect of a

change in a power supply voltage on the D/A converter

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

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.

FIGURE 2. Power Supply Rejection vs Power Supply Ripple

Frequency.

Power Supply Ripple Frequency (Hz)

1

10

100

1k

10k

100k

0.030

0.025

0.020

0.015

0.01

0.005

0

–15V Supply

+15V

Supply

+5V

Supply

REFERENCE SUPPLY

All models have an internal low-noise +6.3V reference

voltage derived from an on-chip buried zener diode. This

reference voltage, available to the user, has a tolerance of

±5% (KH models) and ±1% (BH models). A minimum of

1.5mA is available for external loads. Since the output

impedance of the reference output is typically 1W, the

external load should remain constant.

If a varying load is to be driven by the reference supply, an

external buffer amplifier is recommended to drive the load

in order to isolate the bipolar offset (connected internally to

the reference) from load variations.

OPERATING INSTRUCTIONS

POWER SUPPLY CONNECTIONS

For optimum performance and noise rejection, power sup-

ply 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 part. A

0.001

µF to 0.01µF ceramic capacitor should be connected

from Gain Adjust to Common to prevent noise pickup. Refer

to Figures 4 and 5 for the relationship of zero and gain

adjustments to unipolar and bipolar D/A converters.

FIGURE 3. Equivalent Resistances.

≡

180k

Ω

180k

Ω

3.9M

Ω

10k

Ω

Digital Input

H

Input =

0000

H

Input =

FFFF

Gain Adjust

Rotates

the Line

Range

of Gain

Adjust

1LSB

+ Full

Scale

Range of

Zero Adjust

Zero Adjust

Translates

the Line

FIGURE 4. Relationship of Zero and Gain Adjustments for

Unipolar D/A Converters, DAC701.

Digital Input

H

Input =

FFFF

Gain

Adjust

Rotates

the Line

Range

of Gain

Adjust

1LSB

+ Full

Scale

– Full

Scale

Range

and

Offset

Adjust

Offset

Adjust

Translates

the Line

H

Input =

0000

MSB on All

FIGURE 5. Relationship of Zero and Gain Adjustments for

Bipolar D/A Converters, DAC702 and DAC703.