Table 4. unipolar code table – Rainbow Electronics MAX5231 User Manual

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Digital Feedthrough

Digital feedthrough is noise generated on the DAC’s
output when any digital input transitions. Proper board
layout and grounding significantly reduce this noise,
but there is always some feedthrough caused by the
DAC itself.

Unipolar Output

Figure 7 shows the MAX5230/MAX5231 configured for
unipolar, rail-to-rail operation. The MAX5231 produces
a 0 to 4.095V output, while the MAX5230 produces 0 to
2.0475V output. Table 4 lists the unipolar output codes.

Digital Calibration and

Threshold Selection

Figure 8 shows the MAX5230/MAX5231 in a digital cali-
bration application. With a bright light value applied to
the photodiode (on), the DAC is digitally ramped until it
trips the comparator. The microprocessor (µP) stores
this “high” calibration value. Repeat the process with a
dim light (off) to obtain the dark current calibration. The
µP then programs the DAC to set an output voltage at
the midpoint of the two calibrated values. Applications
include tachometers, motion sensing, automatic read-
ers, and liquid clarity analysis.

Sharing a Common DIN Line

Several MAX5230/MAX5231s may share one common
DIN signal line (Figure 9). In this configuration, the data
bus is common to all devices; data is not shifted through
a daisy-chain. The SCLK and DIN lines are shared by all
devices, but each IC needs its own dedicated CS line.

Daisy-Chaining Devices

Any number of MAX5230/MAX5231s can be daisy-
chained by connecting the serial data output (DOUT) of
one device to the digital input (DIN) of the following
device in the chain (Figure 10).

MAX5230/MAX5231

3V/5V, 12-Bit, Serial Voltage-Output Dual DACs

with Internal Reference

______________________________________________________________________________________

Table 4. Unipolar Code Table

DAC CONTENTS

ANALOG OUTPUT (V)

MSB

LSB

MAX5230

MAX5231

1111 1111 1

111 (0)

2.04750

4.0950

1000 0000 0

001 (0)

1.02425

2.0485

1000 0000 0

000 (0)

1.02375

2.0475

0111 1111 1

111 (0)

1.02325

2.0465

0000 0000

001 (0)

0.00050

0.0010

0000 0000 0

000 (0)

DAC_

MAX5230
MAX5231

REF

5V/3V

GAIN = 1.6384V/V

OUT_

OS_

121k

Ω

77.25k

Ω

AGND

DGND

Figure 7. Unipolar Output Circuit (Rail-to-Rail)