Preliminary Technical Data

AD5040/AD5060

Rev. PrC | Page 15 of 17

used. When data is to be transmitted to the AD5040/AD5060,

P3.3 is taken low. The 80C51/80L51 transmits data only in 8-bit

bytes; thus only eight falling clock edges occur in the transmit

cycle. To load data to the DAC, P3.3 is left low after the first

eight bits are transmitted, and a second write cycle is initiated

to transmit the second byte of data. P3.3 is taken high following

the completion of this cycle. The 80C51/80L51 outputs the

serial data in a format which has the LSB first. The

AD5040/AD5060 requires its data with the MSB as the first bit

received. The 80C51/80L51 transmit routine should take this

into account.

Figure 27. AD5040/AD5060 to 80C51/80L51 Interface

AD5040/AD5060 to Microwire Interface

Figure 28 shows an interface between the AD5040/AD5060 and

any microwire compatible device. Serial data is shifted out on

the falling edge of the serial clock and is clocked into the

AD5040/AD5060 on the rising edge of the SK.

Figure 28. AD5040/AD5060 to MICROWIRE Interface

APPLICATIONS

Choosing a Reference for the AD5040/AD5060.

To achieve the optimum performance from the AD5060,

thought should be given to the choice of a precision voltage

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

REFIN. The voltage on the reference input is used to supply the

positive input to the Dac . Therefore any error in the reference

will be reflected in the Dac.

There are 4 possible sources of error 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 will lead 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 the ADR425 allow a system designer

to trim system errors out 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 error.

Figure 29. ADR425 as Reference to AD5040. ADR420 can be

used for AD5060.

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 co-efficient of a references output voltage

affect INL,DNL TUE. A reference with a tight temperature co-

efficient specification should be chosen to reduce temperatue

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. Choosing a reference with as low an output noise

voltage as practical for the system noise resolution required is

important. Precision voltage references such as the ADR435

produce low output noise in the 0.1-10Hz region. Examples of

some recommended precision references for use as supply to

the AD5060 are shown in the figure below..

Part list of precision references for use with

AD5040/AD5060.

Part No.

Initial

Accuracy

(mV max)

Temp Drift

(ppm

0.1-10Hz Noise

(uV p-p typ)

ADR420

+/-6

3

1.75

ADR425

+/-6

3

3.4

ADR02

+/-5

3

15

ADR395

+/-6

25

5

Bipolar Operation Using the AD5040/AD5060

The AD5040/AD5060 has been designed for single-supply

operation but a bipolar output range is also possible using the

circuit in Figure 30. The circuit below will give an output

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

output is achievable using an AD820 or an OP295 as the output

amplifier.

The output voltage for any input code can be calculated as

follows: