2.0 Applications Information

(Continued)

num electrolytic capacitors are typically not a good choice

due to their large size and have ESR values that may be too

high at low temperatures.

2.3 BIPOLAR OPERATION

The DAC101S101 is designed for single supply operation

and thus has a unipolar output. However, a bipolar output

may be obtained with the circuit in Figure 13. This circuit will

amplifier should be used if the amplifier supplies are limited

The output voltage of this circuit for any code is found to be

V

where D is the input code in decimal form. With V

R1 = R2,

V

A list of rail-to-rail amplifiers suitable for this application are

indicated in Table 2.

TABLE 2. Some Rail-to-Rail Amplifiers

AMP

PKGS

Typ V

OS

Typ I

SUPPLY

LMC7111

DIP-8

SOT23-5

0.9 mV

25 µA

LM7301

SO-8

SOT23-5

0.03 mV

620 µA

LM8261

SOT23-5

0.7 mV

1 mA

2.4 LAYOUT, GROUNDING, AND BYPASSING

For best accuracy and minimum noise, the printed circuit

board containing the DAC101S101 should have separate

analog and digital areas. The areas are defined by the

locations of the analog and digital power planes. Both of

these planes should be located in the same board layer.

There should be a single ground plane. A single ground

plane is preferred if digital return current does not flow

through the analog ground area. Frequently a single ground

plane design will utilize a "fencing" technique to prevent the

mixing of analog and digital ground current. Separate ground

planes should only be utilized when the fencing technique is

inadequate. The separate ground planes must be connected

in one place, preferably near the DAC101S101. Special care

is required to guarantee that digital signals with fast edge

rates do not pass over split ground planes. They must al-

ways have a continuous return path below their traces.

The DAC101S101 power supply should be bypassed with a

10µF and a 0.1µF capacitor as close as possible to the

device with the 0.1µF right at the device supply pin. The

10µF capacitor should be a tantalum type and the 0.1µF

capacitor should be a low ESL, low ESR type. The power

supply for the DAC101S101 should only be used for analog

circuits.

Avoid crossover of analog and digital signals and keep the

clock and data lines on the component side of the board. The

clock and data lines should have controlled impedances.

20154117

FIGURE 13. Bipolar Operation

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