AD5308/AD5318/AD5328
Rev. F | Page 21 of 28
APPLICATIONS INFORMATION
TYPICAL APPLICATION CIRCUIT
The AD5308/AD5318/AD5328 can be used with a wide range
of reference voltages where the devices 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, ADR381, and REF192 (2.5 V references). For 2.5 V
operation, a suitable external reference is the AD589 or the
AD1580 (1.2 V band gap references). Figure 40 shows a typical
setup for the AD5308/AD5318/AD5328 when using an external
reference.
02812-040
AD5308/AD5318/
AD5328
GND
DIN
SYNC
SERIAL
INTERFACE
V
OUT
EXT
REF
0.1μF
V
REF
ABCD
V
REF
EFGH
D780/ADR3811/REF192
ITH V
DD
= 5V OR
D589/AD1580 WITH
DD
= 2.5V
V
DD
= 2.5V TO 5.5V
V
IN
10μF
1μF
SCL
V
OUT
A
V
OUT
G
V
OUT
B
V
OUT
H
Figure 40. AD5308/AD5318/AD5328 Using a 2.5 V or 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
. As this supply can be noisy
and not very accurate, the AD5308/AD5318/AD5328 can be
powered from a voltage reference. For example, using a 5 V
reference, such as the REF195, works because the REF195
outputs a steady supply voltage for the AD5308/AD5318/
AD5328. The typical current required from the REF195 is a
1 A supply current and ≈ 112 A into the reference inputs (if
unbuffered); 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 a10 k
load on each output) is
1.22 mA + 8(5 V/10 k) = 5.22 mA
The load regulation of the REF195 is typically 2.0 ppm/mA,
which results in an error of 10.4 ppm (52 V) for the 5.22 mA
current drawn from it. This corresponds to a 0.003 LSB error at
8 bits and 0.043 LSB error at 12 bits.
BIPOLAR OPERATION USING THE
AD5308/AD5318/AD5328
The AD5308/AD5318/AD5328 have been designed for single-
supply operation, but a bipolar output range is also possible
using the circuit in Figure 41. This circuit gives an output
voltage range of ±5 V. Rail-to-rail operation at the amplifier
output is achievable using an AD820, the AD8519, or an OP196
as the output amplifier.
02812-041
+5V
–5V
AD820/
AD8519/
OP196
10μF
+6V TO +16V
0.1μF
R1
10kΩ
±5V
R2
10kΩ
GND
GND
V
OUT
REF192
+5V
SERIAL
INTERFACE
SCLK
SYNC
DIN
1
μ
F
AD5308/
AD5318/
AD5328
V
REF
ABCD
V
REF
B
V
OUT
C
V
OUT
B
V
OUT
A
V
OUT
H
V
IN
V
DD
Figure 41. Bipolar Operation with the AD5308/AD5318/AD5328
The output voltage for any input code can be calculated as
follows:
()
()
R1RREFIN
R1
RR1DREFIN
V
N
OUT
/2
22/
×−
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
+××
=
where:
D is the decimal equivalent of the code loaded to the DAC.
N is the DAC resolution.
REFIN is the reference voltage input.
with
REFIN = 5 V , R1 = R2 = 10 k
)
VDV
N
OUT
52/10 −×=
OPTO-ISOLATED INTERFACE FOR PROCESS
CONTROL APPLICATIONS
The AD5308/AD5318/AD5328 have a versatile 3-wire serial
interface, making them ideal for generating accurate voltages in
process control and industrial applications. Due to noise and
safety requirements, or distance, it may be necessary to isolate
the AD5308/AD5318/AD5328 from the controller. This can
easily be achieved by using opto-isolators that provide isolation
in excess of 3 kV. The actual data rate achieved may be limited
by the type of optocouplers chosen. The serial loading structure
of the AD5308/AD5318/AD5328 makes them ideally suited for
use in opto-isolated applications. Figure 42 shows an opto-
isolated interface to the AD5308/AD5318/AD5328 where DIN,
SCLK, and
SYNC
are driven from optocouplers. The power
supply to the part also needs to be isolated. This is done by
using a transformer. On the DAC side of the transformer, a 5 V
regulator provides the 5 V supply required for the AD5308/
AD5318/AD5328.
