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AD7302BR

2.7 V to 5.5 V, Parallel Input Dual Voltage Output 8-Bit DAC

Analog Devices 

␣ ␣ VREF is the voltage applied to the external REFIN pin when

the external reference is selected and is VDD/2 if the

internal reference is used.

Table I. Output Voltage for Selected Input Codes

Digital Input

MSB . . . LSB

Analog Output

1111 1111

1111 1110

1000 0001

1000 0000

0111 1111

0000 0001

0000 0000

2 × 255/256 × VREF V

2 × 254/256 × VREF V

2 × 129/256 × VREF V

VREF V

2 × 127/256 × VREF V

2 × VREF/256␣ V

0V

2.VREF

VREF

0

VDD = 3 TO 5V

0.1µF 10µF

AD7302

REF IN

VDD AGND DGND

VOUTA

AD7302

CLR

PD

VOUTB

D7–D0

A/B CS WR LDAC

VDD

DATA BUS CONTROL INPUTS

VOUTA

VOUTB

Figure 27. Typical Configuration Selecting the Internal

Reference

Figure 28 shows a typical setup for the AD7302 when using an

external reference. The reference range for the AD7302 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. There is a gain of two from input to output

on the AD7302. 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.

VDD = 3 TO 5V

0.1µF 10µF

DAC INPUT

CODE

00

01

7F 80 81

FE FF

Figure 26. DAC Transfer Function

Figure 27 shows a typical setup for the AD7302 when using its

internal reference. The internal reference is selected by tying the

REFIN pin to VDD. Internally in the reference section there is a

reference detect circuit that will select the internal VDD/2 based

on the voltage connected to the REFIN pin. If REFIN is within

a threshold voltage of a PMOS device (approximately 1 V) of

VDD the internal reference is selected. When the REFIN voltage

is more than 1 V below VDD, the externally applied voltage at

this pin is used as the reference for the DAC. The internal

reference on the AD7302 is VDD/2, the output current to voltage

converter within the AD7302 provides a gain of two. Thus the

output range of the DAC is from 0 V to VDD, based on Table I.

VIN

EXT REF VOUT

GND

0.1µF

AD780/REF192

WITH VDD = 5V

OR

VDD

AD589 WITH VDD = 3V

REF IN

CLR

PD

D7–D0

VDD AGND DGND

VOUTA

AD7302

VOUTB

A/B CS WR LDAC

DATA BUS CONTROL INPUTS

VOUTA

VOUTB

Figure 28. Typical Configuration Using An External

Reference

REV. 0

–11–

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