AD5066 datasheet(19/20 Pages) AD

19 / 20 page

Preliminary Technical Data

AD5066

Rev. PrB | Page 19 of 20

APPLICATIONS

USING A REFERENCE AS A POWER SUPPLY FOR

THE AD5066

Because the supply current required by the AD5066 is extremely

low, an alternative option is to use a voltage reference to supply

the required voltage to the parts (see Figure 14). 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 AD5066. If the low dropout REF195 is used, it

must supply 500 μA of current to the AD5066, 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.

AD5066

THREE-WIRE

SERIAL

INTERFACE

SYNC

SCLK

DIN

15V

VOUT =0VTO 5V

VDD

REF195

Figure 14. REF195 as Power Supply to the AD5025/45/65

BIPOLAR OPERATION USING THE AD5066

The AD5066 has been designed for single-supply operation,

but a bipolar output range is also possible using the circuit in

Figure 15. 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.

THREE-WIRE

SERIAL

INTERFACE

R2 = 10kΩ

+5V

–5V

AD820/

OP295

+5V

AD5066

VDD

VOUT

R1 = 10kΩ

±5V

0.1µF

10µF

Figure 15. Bipolar Operation with the AD5066

USING THE AD5066 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 AD5066 uses a 3-wire serial logic interface, so the

ADuM1300 three-channel digital isolator provides the required

isolation (see Figure 16). The power supply to the part also

needs to be isolated, which 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 AD5066.

0.1µF

REGULATOR

GND

DIN

SYNC

SCLK

POWER

10µF

SDI

SCLK

DATA

AD5066

VOUT

VOB

VOA

VOC

VDD

VIC

VIB

VIA

ADuM1300

Figure 16. AD5025/45/65 with a Galvanically Isolated Interface

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