DAC8248

–13–

REV. B

loading the appropriate DAC’s digital inputs with 0000 0000

0000 and adjusting the op amp’s offset voltage to 0 V. It is rec-

ommended that the op amp offset voltage be adjusted to less

than 10% of 1 LSB (244

µV), and over the operating tempera-

ture range of interest. This will ensure the DAC’s monotonicity

and minimize gain and linearity errors.

BIPOLAR OPERATION

The bipolar (offset binary) 4-quadrant configuration using the

DAC8248 is shown in Figure 8, and the corresponding code is

shown in Table II. The circuit makes use of the OP470, a quad

op amp (use four OP42s for applications requiring higher

speeds).

the value of R5 and R8, and thus eliminating resistors R1, R2,

R3, and R4. If resistors R1 through R4 are omitted, then R5, R6,

R7 (R8, R9, and R10 for DAC B) should be ratio-matched to

0.01% to keep gain error within data sheet specifications. The re-

sistors should have identical temperature-coefficients if operating

over the full temperature range.

Zero and full-scale are adjusted in one of two ways and are at

the users discretion. Zero-output is adjusted by loading the ap-

propriate DAC’s digital inputs with 1000 0000 0000 and vary-

If R1, R2 (R3, R4 for DAC B) are omitted, then zero output

can be adjusted by varying R6, R7 ratios (R9, R10 for DAC B).

Full-scale is adjusted by loading the appropriate DAC’s digital

inputs with 1111 1111 1111 and varying R5 (R8 for DAC B).

Table II. Bipolar (Offset Binary) Code Table

(Refer to Figure 8)

Binary Number in

DAC Register

MSB

LSB

(DAC A or DAC B)

1111 1111 1111

2047

2048









1000 0000 0001

1

2048









1000 0000 0000

0 V

0111 1111 1111

1

2048









0000 0000 0000

2048

2048









NOTE:

1 LSB=(2

1

2048

SINGLE SUPPLY OPERATION

CURRENT STEERING MODE

Because the DAC8248’s R-2R resistor ladder terminating resis-

tor is internally connected to AGND, it lends itself well for

single supply operation in the current steering mode configura-

tion. This means that AGND can be raised above system

Figure 8. Bipolar Configuration (4-Quadrant Multiplication)