AD7846APZ datasheet(13/24 Pages) AD

13 / 24 page

AD7846

Rev. G | Page 13 of 24

UNIPOLAR BINARY OPERATION

Figure 23 shows the AD7846 in the unipolar binary circuit

configuration. The DAC is driven by the AD586 +5 V reference.

Because RIN is tied to 0 V, the output amplifier has a gain of 2

and the output range is 0 V to +10 V. If a 0 V to +5 V range is

required, RIN should be tied to VOUT, configuring the output

stage for a gain of 1. Table 8 gives the code table for the circuit

of Figure 23.

RIN

VOUT

DGND

+15V

+5V

VCC

VDD

VREF+

VREF–

10kΩ

1µF

SIGNAL

GROUND

–15V

*ADDITIONAL PINS

OMITTED FOR CLARITY

AD7846*

AD586

VOUT

(0V TO +10V)

VSS

Figure 23. Unipolar Binary Operation

Table 8. Code Table for Figure 23

Binary Number in DAC Latch

MSB

LSB1

Analog Output (VOUT)

1111 1111 1111 1111

+10 (65,535/65,536) V

1000 0000 0000 0000

+10 (32,768/65,536) V

0000 0000 0000 0001

+10 (1/65,536) V

0000 0000 0000 0000

0 V

1 LSB = 10 V/216 = 10 V/65,536 = 152 μV.

Offset and gain can be adjusted in Figure 23 as follows:

•

To adjust offset, disconnect the VREF− input from 0 V, load

the DAC with all 0s, and adjust the VREF− voltage until VOUT

= 0 V.

•

For gain adjustment, the AD7846 should be loaded with all

1s and R1 adjusted until VOUT = 10 (65,535)/(65,536) =

9.999847 V. If a simple resistor divider is used to vary the

VREF− voltage, it is important that the temperature

coefficients of these resistors match that of the DAC input

resistance (−300 ppm/°C). Otherwise, extra offset errors are

introduced over temperature. Many circuits do not require

these offset and gain adjustments. In these circuits, R1 can

be omitted. Pin 5 of the AD586 can be left open circuit and

Pin 8 (VREF−) of the AD7846 tied to 0 V.

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