
AD5025/AD5045/AD5065
Rev. 0 | Page 24 of 28
APPLICATIONS INFORMATION
USING A REFERENCE AS A POWER SUPPLY FOR
THE AD5025/AD5045/AD5065
Because the supply current required by the AD5025/AD5045/
AD5065 is extremely low, an alternative option is to use a voltage
reference to supply the required voltage to the parts (see
Figure 50).
This is especially useful if the power supply is quite noisy or if
the system supply voltages are at some value other than 5 V or
3 V, for example, 15 V. The voltage reference outputs a steady
supply voltage for the AD5025/AD5045/AD5065. If the low
dropout
REF195 is used, it must supply 500 μA of current to
the AD5025/AD5045/AD5065 with no load on the output of
the DAC. When the DAC output is loaded, the
REF195 also needs
to supply the current to the load. The total current required
(with a 5 kΩ load on the DAC output) is
500 μA + (5 V/5 kΩ) = 1.5 mA
The load regulation of the
REF195 is typically 2 ppm/mA,
which results in a 3 ppm (15 μV) error for the 1.5 mA current
drawn from it. This corresponds to a 0.196 LSB error.
SYNC
SCLK
DIN
15V
5V
VOUTx = 0V TO 5V
VDD
REF195
AD5025/
AD5045/
AD5065
3-WIRE
SERIAL
INTERFACE
06
84
4-
0
16
Figure 50. REF195 as Power Supply to the AD5025/AD5045/AD5065
BIPOLAR OPERATION USING THE
AD5025/AD5045/AD5065
The AD5025/AD5045/AD5065 is designed for single-supply
operation, but a bipolar output range is also possible using the
circuit in
Figure 51. The circuit gives 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:
R1
R2
V
R1
R2
R1
D
V
DD
O
536
,
65
where D represents the input code in decimal (0 to 65,535).
With VDD = 5 V, R1 = R2 = 10 kΩ,
V
5
536
,
65
10
D
V
O
This is an output voltage range of ±5 V, with 0x0000 corre-
sponding to a 5 V output, and 0xFFFF corresponding to a
+5 V output.
3-WIRE
SERIAL INTERFACE
R2 = 10k
+5V
AD820/
OP295
+5V
AD5025/
AD5045/
AD5065
VDD
VOUT
R1 = 10k
±5V
0.1F
10F
–5V
0
68
44
-01
7
Figure 51. Bipolar Operation with the AD5025/AD5045/AD5065
USING THE AD5025/AD5045/AD5065 WITH A
GALVANICALLY ISOLATED INTERFACE
In process control applications in industrial environments, it is
often necessary to use a galvanically isolated interface to protect
and isolate the controlling circuitry from any hazardous common-
mode voltages that can occur in the area where the DAC is
functioning. iCoupler provides isolation in excess of 2.5 kV.
The AD5025/AD5045/AD5065 use a 3-wire serial logic interface,
so the
ADuM1300 three-channel digital isolator provides the
required isolation (see
Figure 52). The power supply to the part
also needs to be isolated, which is achieved by using a transformer.
On the DAC side of the transformer, a 5 V regulator provides the
5 V supply required for the AD5025/AD5045/AD5065.
0.1F
GND
DIN
SYNC
SCLK
POWER
10F
SDI
SCLK
DATA
AD5025/
AD5045/
AD5065
VOUTx
VOB
VOA
VOC
VDD
VIC
VIB
VIA
ADuM1300
5V
REGULATOR
06
84
4-
0
18
Figure 52. AD5025/AD5045/AD5065 with a Galvanically Isolated Interface