
Preliminary Technical Data
AD5040/AD5060
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.
Rev. PrC | Page 15 of 17
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)
ADR420
+/-6
3
ADR425
+/-6
3
ADR02
+/-5
3
ADR395
+/-6
25
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:
Temp Drift
(ppm
o
C max)
0.1-10Hz Noise
(uV p-p typ)
1.75
3.4
15
5