Daisy-Chaining Devices

The serial output, DOUT, allows cascading of two or

more DACs. The data at DIN appears at DOUT,

delayed by 16 clock cycles plus one clock width. For

low power, DOUT is a CMOS output that does not

require an external pull-up resistor. DOUT does not go

into a high-impedance state when

CS is high. DOUT

changes on SCLK’s falling edge when

CS is low. When

CS is high, DOUT remains in the state of the last data

bit.

Any number of MAX531/MAX538/MAX539 DACs can

be daisy-chained by connecting the DOUT of one

device to the DIN of the next device in the chain. For

Unipolar Configuration

unipolar output) by connecting BIPOFF and RFB to

VOUT (Figure 6). The converter operates from either sin-

gle or dual supplies in this configuration. See Table 1 for

the DAC-latch contents (input) vs. the analog VOUT

MAX538 is internally configured for unipolar gain = +1

operation.

by connecting BIPOFF to AGND and RFB to VOUT

(Figure 7). Table 2 shows the DAC-latch contents vs.

VOUT. The MAX531 operates from either single or dual

ured for unipolar gain = +2 operation.

Bipolar Configuration

A bipolar range is set up by connecting BIPOFF to

REFIN and RFB to VOUT, and operating from dual

(±5V) supplies (Figure 8). Table 3 shows the DAC-latch

contents (input) vs. VOUT (output). In this range,

Four-Quadrant Multiplication

The MAX531 can be used as a four-quadrant multiplier

by connecting BIPOFF to REFIN and RFB to VOUT,

using (1) an offset binary digital code, (2) bipolar power

supplies, using dual power supplies, and (3) a bipolar

- 2V, as shown in Figure 9.

where “G” is the gain (+1 or +2) and “D” is the binary

4096. This formula is precise for unipolar operation.

However, for bipolar, offset binary operation, the MSB is

really a polarity bit. No resolution is lost, as there are

the same number of steps. The output voltage, howev-

er, has been shifted from a range of, for example, 0V to

4.096V (G = +2) to a range of -2.048V to +2.048V.

Keep in mind that when using the DAC as a four-quad-

rant multiplier, the scale is skewed. Negative full scale

+5V, Low-Power, Voltage-Output,

Serial 12-Bit DACs

10

______________________________________________________________________________________

MAX531

CONNECT BIPOFF

TO VOUT FOR G = 1,

TO AGND FOR G = 2,

OR TO REFIN FOR

BIPOLAR GAIN

INVERTED

R-2R DAC

DIN

DOUT

SCLK

CS

CLR

2.048V

REFIN

REFOUT

AGND DGND

+5V

0V TO -5V

33

µF

0.1

µF

0.1

µF

2R

2R

BIPOFF

RFB

VOUT

MAX538

MAX539

INVERTED

R-2R DAC

DIN

DOUT

SCLK

CS

REFIN

AGND

+5V

VOUT

MAX539

ONLY

0.1

µF

2R

2R

Figure 3a. MAX531 Typical Operating Circuit

Figure 3b. MAX538/MAX539 Typical Operating Circuit