Low-Power, 13-Bit Voltage-Output DACs

with Serial Interface

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13

The MAX535’s total harmonic distortion plus noise (THD

+ N) is typically less than -77dB (full-scale code), and

the MAX5351’s THD + N is typically less than -72dB

(full-scale code), given a 1Vp-p signal swing and input

frequencies up to 25kHz. The typical -3dB frequency is

650kHz for both devices, as shown in the

Typical

Operating Characteristics graphs.

Digitally Programmable Current Source

The circuit of Figure 12 places an NPN transistor

(2N3904 or similar) within the op-amp feedback loop to

implement a digitally programmable, unidirectional cur-

rent source. This circuit can be used to drive 4–20mA

current loops, which are commonly used in industrial-

control applications. The output current is calculated

with the following equation:

where NB is the numeric value of the DAC’s binary

input code and R is the sense resistor shown in

Figure 12.

MAX535

MAX5351

DAC

REF

OUT

FB

GND

+5V/+3.3V

Figure 8. Unipolar Output Circuit

Table 3. Bipolar Code Table

MAX535

MAX5351

DAC

REF

OUT

10k

10k

GND

+5V/+3.3V

FB

Figure 9. Unipolar Rail-to-Rail Output Circuit

ANALOG OUTPUT

11111

1111

1111

10000

0000

0001

DAC CONTENTS

MSB

LSB

10000

0000

0000

0V

01111

1111

1111

00000

0000

0000

00000

0000

0001

+V

4095

4096

REF









+V

1

4096

REF









-V

1

4096

REF









-V

4095

4096

REF









-V

4096

4096

-V

REF

REF









=