Applications information – Rainbow Electronics MAX534 User Manual

Page 13

MAX534

+5V, Low-Power, 8-Bit Quad DAC

with Rail-to-Rail Output Buffers

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__________Applications Information

DAC Linearity and Voltage Offset

The output buffer can have a negative input offset volt-
age that would normally drive the output negative, but
since there is no negative supply the output stays at 0V
(Figure 9). When linearity is determined using the end-
point method, it is measured between zero code (all
inputs 0) and full-scale code (all inputs 1) after offset
and gain error are calibrated out. However, in single-
supply operation the next code after zero may not
change the output, so the lowest code that produces a
positive output is the lower endpoint.

Power Sequencing

The voltage applied to REF should not exceed V

any time. If proper power sequencing is not possible,
connect an external Schottky diode between REF and
V

to ensure compliance with the absolute maximum

ratings. Do not apply signals to the digital inputs before
the device is fully powered up.

Power-Supply Bypassing

and Ground Management

Connect AGND and DGND together at the IC. This
ground should then return to the highest-quality ground
available. Bypass V

with a 0.1µF capacitor, located

as close to V

and DGND as possible.

Careful PC board layout minimizes crosstalk among
DAC outputs and digital inputs. Figure 10 shows sug-
gested circuit board layout to minimize crosstalk.

Unipolar-Output,

Two-Quadrant Multiplication

In unipolar operation, the output voltages and the refer-
ence input are the same polarity. Figure 11 shows the
MAX534 unipolar configuration, and Table 2 shows the
unipolar code.

DAC CODE

NEGATIVE

OFFSET

OUTPUT

VOLTAGE

Figure 9. Effect of Negative Offset (Single Supply)

OUTC

OUTD

AGND

OUTB

OUTA

REF

SYSTEM GND

Figure 10. Suggested PC Board Layout for Minimizing
Crosstalk (Bottom View)

DAC A

DAC B

DAC C

DAC D

REFAB

MAX534

OUTA

OUTB

OUTC

OUTD

SERIAL

INTERFACE

NOT SHOWN

REFERENCE INPUT

+3V

AGND

DGND

Figure 11. Unipolar Output Circuit