Datasheet

AD5302/AD5312/AD5322
Rev. D | Page 18 of 24
APPLICATIONS INFORMATION
TYPICAL APPLICATION CIRCUIT
The AD5302/AD5312/AD5322 can be used with a wide range
of reference voltages, especially if the reference inputs are
configured to be unbuffered, in which case the devices offer full,
one-quadrant multiplying capability over a reference range of
0 V to V
DD
. More typically, the AD5302/AD5312/AD5322 can
be used with a fixed, precision reference voltage. Figure 38
shows a typical setup for the AD5302/AD5312/AD5322
when using an external reference. If the reference inputs are
unbuffered, the reference input range is from 0 V to V
DD
, but if
the on-chip reference buffers are used, the reference range is
reduced. Suitable references for 5 V operation are the AD780
and REF192 (2.5 V references). For 2.5 V operation, a suitable
external reference would be the REF191, a 2.048 V reference.
SCLK
DIN
GND
AD5302/AD5312/
AD5322
SERIAL
INTERFACE
EXT
REF
00928-038
AD780/REF192
WITH V
DD
= 5V
OR REF191 WITH
V
DD
= 2.5V
V
OUT
SYNC
V
OUT
A
V
OUT
B
V
REF
A
V
REF
B
1µF
V
DD
= 2.5V to 5.5
V
V
DD
Figure 38. AD5302/AD5312/AD5322 Using External Reference
If an output range of 0 V to V
DD
is required when the reference
inputs are configured as unbuffered (for example, 0 V to 5 V),
the simplest solution is to connect the reference inputs to V
DD
.
As this supply cannot be very accurate and can be noisy, the
AD5302/AD5312/AD5322 can be powered from the reference
voltage, for example, a 5 V reference such as the REF195, as
shown in Figure 39. The REF195 outputs a steady supply
voltage for the AD5302/AD5312/AD5322. The current required
from the REF195 is 300 A supply current and approximately
30 A into each reference input. This is with no load on the
DAC outputs. 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
mA36.1
k10
V5
2A360 =
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
Ω
+
The load regulation of the REF195 is typically 2 ppm/mA,
which results in an error of 2.7 ppm (13.5 V) for the 1.36 mA
current drawn from it. This corresponds to a 0.0007 LSB error
at eight bits and a 0.011 LSB error at 12 bits.
SCLK
DIN
GND
AD5302/AD5312/
AD5322
SERIAL
INTERFACE
REF195
00928-039
V
OUT
SYNC
V
OUT
A
V
OUT
B
V
DD
V
REF
A
1µF
6V to 16
V
GND
V
IN
V
REF
B
0.1µF 10µF
Figure 39. Using a REF195 as Power and Reference to the
AD5302/AD5312/AD5322
BIPOLAR OPERATION USING THE
AD5302/AD5312/AD5322
The AD5302/AD5312/AD5322 are designed for single-supply
operation, but bipolar operation is also achievable using the
circuit shown in Figure 40. This circuit is configured to achieve
an output voltage range of –5 V < V
OUT
< +5 V. Rail-to-rail
operation at the amplifier output is achievable using an AD820
or OP295 as the output amplifier.
SCLK
DIN
GND
AD5302/AD5312/
AD5322
SERIAL
INTERFACE
REF195
00928-040
V
OUT
SYNC
V
OUT
A/B
V
REF
A/B
1µF
GND
V
IN
6V to 16V
0.1µF 10µF
V
DD
V
DD
= 5
V
+5V
–5V
R2
10kΩ
AD820/
OP295
R1
10kΩ
±5V
Figure 40. Bipolar Operation Using the AD5302/AD5312/AD5322
The output voltage for any input code can be calculated as
follows:
(
)
()
()
1/2
1
212/
RRV
R
RRDV
V
REF
N
REF
OUT
×−
⎥
⎦
⎤
⎢
⎣
⎡
+××
=
where:
D is the decimal equivalent of the code loaded to the DAC.
N is the DAC resolution.
V
REF
is the reference voltage input.
If V
REF
= 5 V, R1 = R2 = 1 k, and V
DD
= 5 V:
(
)
V52/10 −×=
N
OUT
DV