MAX5590 datasheet(30/33 Pages) MAXIM

30 / 33 page

Buffered, Fast-Settling, Octal, 12/10/8-Bit,

Voltage-Output DACs

______________________________________________________________________________________

Applications Information

Unipolar Output

Figure 7 shows the unity-gain MAX5590 in a unipolar

output configuration. Table 24 lists the unipolar out-

put codes.

Bipolar Output

The MAX5590 outputs can be configured for bipolar

operation, as shown in Figure 8. The output voltage is

given by the following equation:

VOUT_ = VREF x (CODE - 2048) / 2048

where CODE represents the numeric value of the

DAC’s binary input code (0 to 4095 decimal). Table 25

shows digital codes and the corresponding output volt-

age for the Figure 8 circuit.

Configurable Output Gain

The MAX5591/MAX5593/MAX5595 have force-sense

outputs, which provide a direct connection to the invert-

ing terminal of the output op amp, yielding the most

flexibility. The force-sense output has the advantage

that specific gains can be set externally for a given

application. The gain error for the MAX5591/MAX5593/

MAX5595 is specified in a unity-gain configuration (op-

amp output and inverting terminals connected), and

additional gain error results from external resistor

tolerances. The force-sense DACs allow many useful

circuits to be created with only a few simple external

components.

An example of a custom, fixed gain using the

MAX5591’s force-sense output is shown in Figure 9. In

this example, the external reference is set to 1.25V, and

the gain is set to +1.1V/V with external discrete resis-

tors to provide an approximate 0 to 1.375V DAC output

voltage range.

VOUT = [(0.5 x VREF_ x CODE) / 4096] x [1 + (R2 / R1)]

where CODE represents the numeric value of the

DAC’s binary input code (0 to 4095 decimal).

In this example, R2 = 12k

Ω and R1 = 10kΩ to set the

gain = 1.1V/V.

VOUT = [(0.5 x 1.25V x CODE) / 4096] x 2.2

Table 25. Bipolar Code Table (Gain = +1)

DAC CONTENTS

MSB

LSB

ANALOG OUTPUT

1111

+VREF (2047 / 2048)

1000

0000

0001

+VREF (1 / 2048)

1000

0000

0111

1111

-VREF (1 / 2048)

0000

0001

-VREF (2047 / 2048)

0000

-VREF (2048 / 2048) = -VREF

Figure 8. Bipolar Output Circuit

MAX5590

DAC_

REF

OUT_

10k

Ω

10k

Ω

V+

V-

VOUT

MAX5591

DAC_

REF

OUT_

FB_

R2 = 12k

Ω

0.1%

25ppm

R1 = 10k

Ω

0.1%

25ppm

Figure 9. Configurable Output Gain

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