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AD5040/AD5060

Rev. A | Page 19 of 24

APPLICATIONS

CHOOSING A REFERENCE FOR THE AD5040/

AD5060

To achieve the optimum performance from the AD5040/

AD5060, carefully choose a precision voltage reference. The

AD5040/AD5060 have just one reference input, VREF. The

voltage on the reference input is used to supply the positive

input to the DAC. Therefore, any error in the reference is

reflected in the DAC.

There are four possible sources of error to consider when

choosing a voltage reference for high accuracy applications:

initial accuracy, ppm drift, long-term drift, and output voltage

noise. Initial accuracy on the output voltage of the DAC leads

to a full-scale error in the DAC. To minimize these errors, a

reference with high initial accuracy is preferred. Also, choosing

a reference with an output trim adjustment, such as an ADR43x

device, allows a system designer to trim out system errors by

setting a reference voltage to a voltage other than the nominal.

The trim adjustment can also be used at temperature to trim

out any errors.

Because the supply current required by the AD5040/AD5060 is

extremely low, the parts are ideal for low supply applications.

The ADR395 voltage reference is recommended. This requires

less than 100 μA of quiescent current and can, therefore, drive

multiple DACs in one system, if required. It also provides very

good noise performance at 8 μV p-p in the 0.1 Hz to 10 Hz range.

SYNC

SCLK

DIN

VOUT = 0V TO 5V

ADR395

3-WIRE

SERIAL

INTERFACE

AD5040/

AD5060

Figure 50. ADR395 as Reference to AD5060/AD5040

Long-term drift is a measure of how much the reference drifts

over time. A reference with a tight long-term drift specification

ensures that the overall solution remains relatively stable during

its entire lifetime. The temperature coefficient of a reference

output voltage affects INL, DNL, and TUE. A reference with a

tight temperature coefficient specification should be chosen to

reduce the temperature dependence of the DAC output voltage

on ambient conditions.

In high accuracy applications, which have a relatively low noise

budget, reference output voltage noise needs to be considered. It

is important to choose a reference with as low an output noise

voltage as practical for the system noise resolution required.

Precision voltage references, such as the ADR435, produce low

output noise in the 0.1 Hz to 10 Hz region. Table 8 shows

examples of recommended precision references for use as a

supply to the AD5040/AD5060.

Table 8. Precision References for the AD5040/AD5060

Part No.

Initial

Accuracy

(mV max)

Temp. Drift

(ppm/°C max)

0.1 Hz to 10 Hz

Noise (μV p-p typ)

ADR435

±2

3 (SO-8)

ADR425

±2

3 (SO-8)

3.4

ADR02

±3

3 (SO-8)

ADR02

±3

3 (SC70)

ADR395

±5

9 (TSOT-23)

BIPOLAR OPERATION USING THE AD5040/

AD5060

The AD5040/AD5060 have been designed for single-supply

operation, but a bipolar output range is also possible using the

circuit in Figure 51. The circuit shown yields an output voltage

range of ±5 V. Rail-to-rail operation at the amplifier output is

achievable using an AD8675/AD820/AD8032 or an OP196/

OP295.

The output voltage for any input code can be calculated as

⎥⎦

⎤

⎢⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

65536

where D represents the input code in decimal (0 to 65536,

AD5060).

With VREF = 5 V, R1 = R2 = 10 kΩ:

65536

−

⎟

⎠

⎞

⎜

⎝

⎛ ×

Using the AD5060, this is an output voltage range of ±5 V

with 0x0000 corresponding to a −5 V output and 0xFFFF

corresponding to a +5 V output .

+5V

μF

R1 = 10k

VOUT

VREF

0.1

μF

3-WIRE

SERIAL

INTERFACE

AD820/

OP295

–

–5V

+5V

R2 = 10k

±5V

AD5040/

AD5060

Figure 51. Bipolar Operation with the AD5040/AD5060

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