Datasheet

AD5724/AD5734/AD5754
Rev. D | Page 29 of 32
• Reference output voltage noise needs to be considered in
high accuracy applications that have relatively low noise
budgets. It is important to choose a reference with as low
an output noise voltage as practical for the required system
resolution. Precision voltage references such as the ADR431
(XFET® design) produce low output noise in the 0.1 Hz to
10 Hz range. However, as the circuit bandwidth increases,
filtering the output of the reference may be required to
minimize the output noise.
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5724/AD5734/AD5754 is
via a serial bus that uses standard protocol compatible with
microcontrollers and DSP processors. The communications
channel is a 3-wire (minimum) interface consisting of a clock
signal, a data signal, and a synchronization signal. The AD5724/
AD5734/AD5754 require a 24-bit data-word with data valid on
the falling edge of SCLK.
For all interfaces, the DAC output update can be initiated
automatically when all the data is clocked in, or it can be
performed under the control of
LDAC
. The contents of the
registers can be read using the readback function.
AD5724/AD5734/AD5754 to Blackfin® DSP Interface
Figure 44 shows how the AD5724/AD5734/AD5754 can be inter-
faced to the Analog Devices Blackfin DSP. The Blackfin has an
integrated SPI port that can be connected directly to the SPI pins
of the AD5724/AD5734/AD5754 and the programmable I/O pins
that can be used to set the state of a digital input such as the
LDAC
pin.
SYNC
ADSP-BF531
AD5724/
AD5734/
AD5754
SCLK
SDIN
SPISELx
SCK
MOSI
LDAC
PF10
06468-012
Figure 44. AD5724/AD5734/AD5754 to Blackfin Interface
Table 28. Some Precision References Recommended for Use with the AD5724/AD5734/AD5754
Part No. Initial Accuracy (mV max) Long-Term Drift (ppm typ) Temp Drift (ppm/°C max) 0.1 Hz to 10 Hz Noise (μV p-p typ)
ADR431 ±1 40 3 3.5
ADR421 ±1 50 3 1.75
ADR03 ±2.5 50 3 6
ADR291 ±2 50 8 8
AD780 ±1 20 3 4