AD5643R datasheet(26/28 Pages) AD

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AD5623R/AD5643R/AD5663R

Rev. A | Page 26 of 28

APPLICATIONS INFORMATION

USING A REFERENCE AS A POWER SUPPLY

Because the supply current required by the AD5623R/AD5643R/

AD5663R is extremely low, an alternative option is to use a

voltage reference to supply the required voltage to the parts (see

Figure 60). 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 AD5623R/AD5643R/ AD5663R.

If the low dropout REF195 is used, it must supply 500 μA of

current to the AD5623R/AD5643R/AD5663R, 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) = 1.25 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.

AD5623R/

AD5643R/

AD5663R

THREE-WIRE

SERIAL

INTERFACE

SYNC

SCLK

DIN

15V

VOUT = 0V TO 5V

VDD

REF195

Figure 60. REF195 as Power Supply to the AD5623R/AD5643R/AD5663R

BIPOLAR OPERATION USING THE AD5663R

The AD5663R has been designed for single-supply operation,

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

Figure 61. 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

AD5663R

VDD

VOUT

R1 = 10kΩ

±5V

0.1µF

10µF

Figure 61. Bipolar Operation with the AD5663R

USING THE AD5663R 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 AD5663R uses a 3-wire serial logic interface, so

the ADuM1300 3-channel digital isolator provides the required

isolation (see Figure 62). 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 AD5663R.

0.1µF

REGULATOR

GND

DIN

SYNC

SCLK

POWER

10µF

SDI

SCLK

DATA

AD5663R

VOUT

VOB

VOA

VOC

VDD

VIC

VIB

VIA

ADuM1300

Figure 62. AD5663R with a Galvanically Isolated Interface

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