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 MAX5232/MAX5233 configured for

unipolar, rail-to-rail operation. The MAX5233 produces

a 0 to 4.092V output, while the MAX5232 produces 0 to

2.046V output. Table 4 lists the unipolar output codes.

Digital Calibration and

Threshold Selection

Figure 8 shows the MAX5232/MAX5233 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 MAX5232/MAX5233s 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 MAX5232/MAX5233s 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).

3V/5V, 10-Bit, Serial Voltage-Output Dual DACs

with Internal Reference

______________________________________________________________________________________

15

Table 4. Unipolar Code Table

DAC CONTENTS

ANALOG OUTPUT (V)

MSB

LSB

MAX5232

MAX5233

1111 1111 11

(000)

2.046

4.092

1000 0000 01

(000)

1.025

2.050

1000 0000 00

(000)

1.023

2.046

0111 1111 11

(000)

1.021

2.042

0000 0000 01

(000)

0.002

0.004

0000 0000 00

(000)

0

0

DAC_

MAX5232

MAX5233

REF

REF

AGND

DGND

5V/3V

OUT_

OS_

121k

Ω

77.25k

Ω

1k

Ω

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

DAC_

MAX5232

MAX5233

REF

REF

AGND

DGND

5V/3V

OUT_

PHOTODIODE

OS_

V+

V+

V-

121k

Ω

77.25k

Ω

1k

Ω

Figure 8. Digital Calibration