AD5644R datasheet(25/28 Pages) AD

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AD5624R/AD5644R/AD5664R

Rev. A | Page 25 of 28

APPLICATIONS

USING A REFERENCE AS A POWER SUPPLY FOR

THE AD5624R/AD5644R/AD5664R

Because the supply current required by the AD5624R/AD5644R/

AD5664R is extremely low, an alternative option is to use a

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

Figure 61). 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 AD5624R/AD5644R/

AD5664R (see Figure 59). If the low dropout REF195 is used, it

must supply 450 μA of current to the AD5624R/AD5644R/

AD5664R 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

450 μA + (5 V/5 kΩ) = 1.45 mA

The load regulation of the REF195 is typically 2 ppm/mA,

resulting in a 2.9 ppm (14.5 μV) error for the 1.45 mA current

drawn from it. This corresponds to a 0.191 LSB error.

3-WIRE

SERIAL

INTERFACE

SYNC

SCLK

DIN

15V

VOUT = 0V TO 5V

VDD

REF195

AD5624R/

AD5644R/

AD5664R

Figure 61. REF195 as Power Supply to the AD5624R/AD5644R/AD5664R

BIPOLAR OPERATION USING THE

AD5624R/AD5644R/AD5664R

The AD5624R/AD5644R/AD5664R has been designed for

single-supply operation, but a bipolar output range is also

possible using the circuit in Figure 62. 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 65536).

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

–5V

AD820/

OP295

+5V

AD5624R/

AD5644R/

AD5664R

VDD

VOUT

R1 = 10kΩ

±5V

0.1µF

10µF

Figure 62. Bipolar Operation with the AD5624R/AD5644R/AD5664R

USING AD5624R/AD5644R/AD5664R 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 might occur in the area where the

DAC is functioning. Isocouplers provide isolation in excess of

3 kV. The AD5624R/AD5644R/AD5664R use a 3-wire serial

logic interface, so the ADuM130x 3-channel digital isolator

provides the required isolation (see Figure 63). 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 AD5624R/

AD5644R/AD5664R.

0.1µF

REGULATOR

GND

DIN

SYNC

SCLK

POWER

10µF

SDI

SCLK

DATA

AD5624R/

AD5644R/

AD5664R

VOUT

VOB

VOA

VOC

VDD

V1C

V1B

V1A

ADuM1300

Figure 63. AD5624R/AD5644R/AD5664R with a Galvanica ly Isolated Interface

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