Datasheet

AD5307/AD5317/AD5327
Rev. C | Page 20 of 28
APPLICATIONS
TYPICAL APPLICATION CIRCUIT
The AD5307/AD5317/AD5327 can be used with a wide range
of reference voltages and offer full, one-quadrant multiplying
capability over a reference range of 0.25 V to V
DD
. More typically,
these devices are used with a fixed precision reference voltage.
Suitable references for 5 V operation are the AD780 and REF192
(2.5 V references). For 2.5 V operation, a suitable external refer-
ence would be the AD589, a 1.23 V band gap reference.
Figure 41
shows a typical setup for the AD5307/AD5317/AD5327 when
using an external reference.
1µF
10µF
SCLK
DIN
GND
AD5307/AD5317/
AD5327
SERIAL
INTERFACE
EXT
REF
02067-041
V
DD
= 2.5V TO 5.5
V
AD780/REF192
WITH V
DD
= 5V
OR AD589 WITH
V
DD
= 2.5V
V
IN
V
OUT
SYNC
V
OUT
A
V
OUT
B
V
OUT
C
V
OUT
D
V
REF
AB
V
REF
CD
0.1µF
Figure 41. AD5307/AD5317/AD5327 Using a 2.5 V External Reference
DRIVING V
DD
FROM THE REFERENCE VOLTAGE
If an output range of 0 V to V
DD
is required when the reference
inputs are configured as unbuffered, the simplest solution is to
connect the reference input to V
DD
. Because this supply can be
noisy and not very accurate, the AD5307/AD5317/AD5327 can
be powered from the reference voltage, for example, from a 5 V
reference such as the REF195, which outputs a steady supply
voltage. The typical current required from the REF195 with no
load on the DAC outputs is 500 A supply current and ≈112 A
into the reference inputs (if unbuffered). When the DAC
outputs are loaded, the REF195 also needs to supply the current
to the loads. The total current required with a 10 k load on
each output is
612 A + 4 (5 V/10 k) = 2.6 mA
The load regulation of the REF195 is typically 2 ppm/mA,
which results in an error of 5.2 ppm (26 V) for the 2.6 mA
current drawn from it. This corresponds to a 0.0013 LSB error
at eight bits and a 0.021 LSB error at 12 bits.
BIPOLAR OPERATION
The AD5307/AD5317/AD5327 are designed for single-supply
operation, but a bipolar output range is also possible using the
circuit shown in
Figure 42. This circuit provides an output
voltage range of 5 V. Rail-to-rail operation at the amplifier
output is achievable by using an AD820 or an OP295 as the
output amplifier.
The output voltage for any input code can be calculated as
follows:
(
)
)/(
1
)(2/
R1R2REFIN
R
R2R1DREFIN
V
N
OUT
×−
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
+××
=
where:
D is the decimal equivalent of the code loaded to the DAC.
N is the DAC resolution.
REFIN is the reference voltage input.
When REFIN = 5 V, R1 = R2 = 10 k,
V
OUT
= (10 × D/2
N
) − 5 V
+5V
AD820/
OP295
±5V
+5V
R1
10kΩ
R2
10kΩ
SCLK
GND
SERIAL
INTERFACE
–5V
+6V TO +16V
AD5307/AD5317/
AD5327
DIN
02067-042
SYNC
V
OUT
A
V
OUT
B
V
OUT
C
V
OUT
D
V
REF
AB
V
REF
CD
10µF
0.1µF
GND
REF195
V
IN
V
OUT
1µF
V
DD
Figure 42. Bipolar Operation with the AD5307/AD5317/AD5327