DAC8222E データシートの表示（PDF） - Analog Devices

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DAC8222E

Dual 12-Bit Double-Buffered Multiplying CMOS D/A Converter

Analog Devices 

DAC8222

* RESISTORS R1 THROUGH R4 ARE ONLY NECESSARY TO TRIM FOR

ABSOLUTE ACCURACY BETTER THAN ؎0.01%, SEE TEXT FOR

COMPLETE DETAILS.

** REGISTERS AND CONTROL CIRCUITRY OMITTED FOR SIMPLICITY.

Figure 24. Unipolar Configuration (Two-Quadrant Multiplication)

APPLICATIONS INFORMATION

UNIPOLAR OPERATION

Figure 24 shows a simple unipolar (2-quadrant multiplication)

circuit using the DAC8222 and OP270 dual op amp (use two

OP42s for higher speeds), and Table II the corresponding code

table. Resistors R1, R2, and R3, R4 are used only if full-scale

gain adjustments are required. Low temperature coefficient

(approximately 50 ppm/°C) resistors or trimmers should be

used. Maximum full-scale error without these resistors for the

top grade device and VREF = ± 10 V is 0.024% and 0.097% for

the low grade. C1 and C2 provide phase compensation to help

reduce overshoot and ringing when high speed op amps are used.

Full-scale adjustment is accomplished by loading the digital

inputs with all 1s and adjusting R1 (or R3) so that

 4095 

VOUT = VREF ×  4096 

Full-scale can also be adjusted by varying VREF voltage, thus

eliminating R1, R2, R3 and R4. Zero adjustment is performed

by setting the DAC’s digital inputs to all 0s and adjusting the op

amp’s offset adjust so that VOUT = 0 V. To maintain monotonic-

ity and minimize gain and linearity errors, it is recommended

that the op amp offset voltage be adjusted to less than 10% of

1 LSB (244 µV) over the operating temperature range of interest.

Table II. Unipolar Binary Code Table (Refer to Figure 24)

Binary Number in

DAC Register

MSB

LSB

Analog Output, VOUT

(DAC A or DAC B)

1111 1111 1111

 4095 

–VREF  4096 

1000 0000 0000

 2048 

–VREF  4096  = –1/2 VREF

0000 0000 0001

0000 0000 0000

 1

–VREF  4096 

0V

NOTE

1

1 LSB = (2–12) (VREF) = 4096 (VREF)

BIPOLAR OPERATION

The bipolar (offset binary) four-quadrant operation configura-

tion using the DAC8222 is shown in Figure 25 and the corre-

sponding code in Table III. The circuit makes use of the OP470

a quad op amp (use four OP42s for higher speeds).

Resistors R1, R2, R3, and R4 may be omitted and full-scale

output voltage may be adjusted by varying VREF or the value

of R5 and R8. If resistors R1, R2, R3, and R4 are omitted,

–10–

REV. C

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