AD5451 datasheet(14/20 Pages) AD

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AD5547/AD5557

Data Sheet

Rev. D | Page 14 of 20

APPLICATIONS INFORMATION

UNIPOLAR MODE

2-Quadrant Multiplying Mode, VOUT = 0 V to –VREF

The AD5547/AD5557 DAC architecture uses a current-steering

R-2R ladder design that requires an external reference and op

amp to convert the unipolar mode of the output voltage to

VOUT = −VREF × D/65,536 (AD5547)

(1)

VOUT = −VREF × D/16,384 (AD5557)

(2)

where D is the decimal equivalent of the input code.

In this case, the output voltage polarity is opposite the VREF

polarity (see Figure 21). Table 7 shows the negative output vs.

code for the AD5547.

Table 7. AD5547 Unipolar Mode Negative Output vs. Code

D in Binary

OUT (V)

1111 1111 1111 1111

–V

REF (65,535/65,536)

1000 0000 0000 0000

–V

REF/2

0000 0000 0000 0001

–V

REF (1/65,536)

0000 0000 0000 0000

LDAC

+2.5V

AD8628

AD5547/AD5557

R1A

16/14 DATA

VDD

RCOMA

ROFSA

RFBA

RFB

ROFS

MSB A0, A1

IOUTA

AGNDA

6.8pF

1µF

0.1µF

VOUTA

VREFA

MSB

A0, A1

LDAC

–V

GND

VOUT

TRIM

ADR03

VIN

+5V

16-/14-BIT

2.5V

1µF

0.1µF

–5V

–2.5V TO 0V

Figure 21. Unipolar 2-Quadrant Multiplying Mode, VOUT = 0 to –VREF

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