Datasheet

MAX5580–MAX5585
Buffered, Fast-Settling, Quad,
12-/10-/8-Bit, Voltage-Output DACs
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Applications Information
Unipolar Output
Figure 7 shows the unity-gain MAX5580 in a unipolar
output configuration. Table 23 lists the unipolar out-
put codes.
Bipolar Output
The MAX5580 outputs can be configured for bipolar
operation, as shown in Figure 8. The output voltage is
given by the following equation:
V
OUT_
= V
REF
x (CODE - 2048) / 2048
where CODE represents the numeric value of the
DAC’s binary input code (0 to 4095 decimal). Table 24
shows digital codes and the corresponding output volt-
age for the circuit in Figure 8.
Configurable Output Gain
The MAX5581/MAX5583/MAX5585 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 MAX5581/MAX5583/
MAX5585 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
MAX5581’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.
V
OUT
= [(0.5 x V
REF_
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 = 12kΩ and R1 = 10kΩ to set the
gain = 1.1V/V:
V
OUT
= [(0.5 x 1.25V x CODE) / 4096] x 2.2
Table 24. Bipolar Code Table (Gain = +1)
DAC CONTENTS
MSB LSB
ANALOG OUTPUT
1111 1111 1111 +V
REF
(2047 / 2048)
1000 0000 0001 +V
REF
(1 / 2048)
1000 0000 0000 0
0111 1111 1111 -V
REF
(1 / 2048)
0000 0000 0001 -V
REF
(2047 / 2048)
0000 0000 0000 -V
REF
(2048 / 2048) = -V
REF
Figure 8. Bipolar Output Circuit
MAX5580
MAX5582
MAX5584
DAC_
REF
10kΩ 10kΩ
V+
V-
V
OUT_
MAX6126
MAX5581
DAC_
REF
OUT_
FB_
R2 = 12kΩ
0.1%
25ppm
R1 = 10kΩ
0.1%
25ppm
MAX6126
Figure 9. Configurable Output Gain