MAX11359A_12 Datasheet, PDF(59/67 Page) Maxim Integrated Products – 16-Bit Data-Acquisition System with ADC, DAC, UPIOs, RTC, Voltage Monitors, and Temp Sensor

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MAX11359A_12 Datasheet, PDF (59/67 Pages) Maxim Integrated Products – 16-Bit Data-Acquisition System with ADC, DAC, UPIOs, RTC, Voltage Monitors, and Temp Sensor

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MAX11359A

16-Bit Data-Acquisition System with ADC, DAC,

UPIOs, RTC, Voltage Monitors, and Temp Sensor

MAX11359A

DAC A

FBA

10kâ¦

OUTA

VREF

DAC_

MAX11359A

FB_

+3.3V

VOUT

OUT_

-3.3V

R2 = R1

VREF = 1.25V

Figure 23. DAC Unipolar Rail-to-Rail Output Circuit

Power Supplies

AVDD and DVDD provide power to the MAX11359A. The

AVDD powers up the analog section, while the DVDD pow-

ers up the digital section. The power supply for both AVDD

and DVDD ranges from +1.8V to +3.6V. Both AVDD and

DVDD must be greater than +1.8V for device operation.

AVDD and DVDD can connect to the same power supply.

Bypass AVDD to AGND with a 10ÂµF electrolytic capacitor

in parallel with a 0.1ÂµF ceramic capacitor, and bypass

DVDD to DGND with a 10ÂµF electrolytic capacitor in paral-

lel with a 0.1ÂµF ceramic capacitor. For improved perfor-

mance, place the bypass capacitors as close to the device

as possible.

ADC Transfer Functions

Figures 20 and 21 provide the ADC transfer functions

for unipolar and bipolar mode. The digital output code

format is binary for unipolar mode and twoâs comple-

ment for bipolar mode. Calculate 1 LSB using the fol-

lowing equations:

1 LSB (Unipolar Mode) = VREF/(Gain x 65,536)

1 LSB (Bipolar Mode) = Â±2VREF/(Gain x 65,536)

where VREF equals the reference voltage at REF and

Gain equals the PGA gain.

Table 22. Unipolar Code

DAC CONTENTS

MSB LSB

1111 1111 11

1000 0000 01

1000 0000 00

0111 1111 11

0000 0000 01

0000 0000 00

ANALOG OUTPUT

+VREF (1023/1024)

+VREF (513/1024)

+VREF (512/1024) = +VREF/2

+VREF (511/1024)

+VREF (1/1024)

Maxim Integrated

Figure 24. DAC Bipolar Output Circuit

In unipolar mode, the output code ranges from 0 to

65,535 for inputs from zero to full-scale. In bipolar

mode, the output code ranges from -32,768 to +32,767

for inputs from negative full-scale to positive full-scale.

DAC Unipolar Output

For a unipolar output, the output voltages and the refer-

ence have the same polarity. Figure 22 shows the

unipolar output circuit of the MAX11359A, which is also

the typical operating circuit for the DAC. Table 22 lists

some unipolar input codes and their corresponding

output voltages.

For larger output swing, see Figure 23. This circuit

shows the output amplifiers configured with a closed-

loop gain of +2V/V to provide 0 to 2.5V full-scale range

with the 1.25V reference.

DAC Bipolar Output

The MAX11359A DAC output can be configured for

bipolar operation using the application circuit in

Figure 24:

VOUT

VREF

â¡â 2N â

â£â¢ââ 1024â â

â¤

1â¥

â¦

where N is the decimal value of the DACâs binary input code.

Table 23 shows digital codes (offset binary) and corre-

sponding output voltages for Figure 24 assuming

R1 = R2.

Table 23. Bipolar Code

DAC CONTENTS

MSB LSB

1111 1111 11

1000 0000 01

1000 0000 00

0111 1111 11

0000 0000 01

0000 0000 00

ANALOG OUTPUT

+VREF (511/512)

+VREF (1/512)

-VREF (1/512)

-VREF (511/512)

-VREF (512/512) = -VREF

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