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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

VOUTx = 0V TO 5V

VDD

REF195

AD5025/

AD5045/

AD5065

3-WIRE

SERIAL

INTERFACE

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:





























































536

where D represents the input code in decimal (0 to 65,535).

With VDD = 5 V, R1 = R2 = 10 kΩ,

536



















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 = 10kΩ

+5V

AD820/

OP295

+5V

AD5025/

AD5045/

AD5065

VDD

VOUT

R1 = 10kΩ

±5V

0.1µF

10µF

–5V

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.

0.1µF

GND

DIN

SYNC

SCLK

POWER

10µF

SDI

SCLK

DATA

AD5025/

AD5045/

AD5065

VOUTx

VOB

VOA

VOC

VDD

VIC

VIB

VIA

ADuM1300

REGULATOR

Figure 52. AD5025/AD5045/AD5065 with a Galvanically Isolated Interface

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