Rainbow-electronics MAX5231 Manual de usuario descargar pdf (Pagina 15)

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

______________________________________________________________________________________ 15

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) 0 0

DAC_

MAX5230

MAX5231

REF

5V/3V

GAIN = 1.6384V/V

OUT_

OS_

121kΩ

77.25kΩ

1kΩ

AGND DGND

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

DAC_

MAX5230

MAX5231

REF

OUT

5V/3V

OUT_

PHOTODIODE

OS_

V+

V-

121kΩ

77.25kΩ

1kΩ

PULLDOWN

AGND DGND

Figure 8. Digital Calibration

1 2 ... 10 11 12 13 14 15 16 17 18

MAX5230/MAX5231 1

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