AD7303BNZ datasheet(12/16 Pages) AD

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AD7303

–12–

REV. 0

AD7303 to Microwire Interface

Figure 29 shows an interface between the AD7303 and any

microwire compatible device. Serial data is shifted out on the

falling edge of the serial clock and is clocked into the AD7303

on the rising edge of the SK.

SCLK

MICROWIRE*

*ADDITIONAL PINS OMITTED FOR CLARITY

SYNC

DIN

AD7303*

Figure 29. AD7303 to Microwire Interface

APPLICATIONS

Typical Application Circuit

Figure 30 shows a typical setup for the AD7303 when using an

external reference. The reference range for the AD7303 is from

1 V to VDD/2 V. Higher values of reference can be incorporated

but will saturate the output at both the top and bottom end of

the transfer function. From input to output on the AD7303

there is a gain of two. Suitable references for 5 V operation are

the AD780 and REF192. For 3 V operation, a suitable external

reference would be the AD589, a 1.23 V bandgap reference.

AD7303

VOUTA

VOUTB

10µF

0.1µF

VDD = +3V TO +5V

VDD

GND

AD780/ REF192

WITH VDD = +5V

AD589 WITH VDD = +3V

REF

SCLK

DIN

SYNC

GND

VOUT

VIN

0.1µF

SERIAL

INTERFACE

EXT

REF

Figure 30. AD7303 Using External Reference

The AD7303 can also be used with its own internally derived

VDD/2 reference. Reference selection is through the INT/EXT

bit of the 16-bit input word. The internal reference, when

selected, is also provided as an output at the REF pin and can

be decoupled at this point with a 0.1

µF capacitor for noise

reduction purposes. AC references can also be applied as exter-

nal references to the AD7303. The AD7303 has limited multi-

plying capability, and a multiplying bandwidth of up to 10 kHz

is achievable.

Bipolar Operation Using the AD7303

The AD7303 has been designed for single supply operation, but

bipolar operation is achievable using the circuit shown in Figure

31. The circuit shown has been configured to achieve an output

voltage range of –5 V < VO < +5 V. Rail-to-rail operation at the

amplifier output is achievable using an AD820 or OP295 as the

output amplifier.

10k

Ω

20k

Ω

10k

Ω

+5V

–5V

±5V

AD7303

VOUTA

10µF

0.1µF

VDD = +5V

VDD

GND

AD780/ REF192

WITH VDD = +5V

AD589 WITH VDD = +3V

REF

SCLK

DIN

SYNC

GND

VOUT

VIN

0.1µF

SERIAL

INTERFACE

EXT

REF

20k

Ω

Figure 31. Bipolar Operation Using the AD7303

The output voltage for any input code can be calculated as

follows:

VO = [(1+R4/R3)*(R2/(R1+R2)*(2*VREF*D/256)] – R4*VREF/R3

where

D is the decimal equivalent of the code loaded to the DAC

and

VREF is the reference voltage input.

With VREF = 2.5 V, R1 = R3 = 10 k

Ω and R2 = R4 = 20K and

VDD = 5 V.

VOUT = (10 × D/256) – 5

Opto-Isolated Interface for Process Control Applications

The AD7303 has a versatile 3-wire serial interface making it

ideal for generating accurate voltages in process control and

industrial applications. Due to noise, safety requirements or dis-

tance, it may be necessary to isolate the AD7303 from the con-

troller. This can easily be achieved by using opto-isolators,

which will provide isolation in excess of 3 kV. The serial loading

structure of the AD7303 makes it ideally suited for use in opto-

isolated applications. Figure 32 shows an opto-isolated interface

to the AD7303 where DIN, SCLK and SYNC are driven from

opto-couplers. In this application the reference for the AD7303

is the internal VDD/2 reference. It is being decoupled at the REF

pin with a 0.1

µF ceramic capacitor for noise reduction purposes.

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