8143 Datasheet, PDF(12/24 Page) Maxwell Technologies – 12-Bit Serial Daisy Chain D/A Converter

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8143 Datasheet, PDF (12/24 Pages) Maxwell Technologies – 12-Bit Serial Daisy Chain D/A Converter

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12-Bit Serial Daisy-Chain D/A Converter

FIGURE 13. EQUIVALENT CIRCUIT (ALL INPUT HIGH)

8143

Dynamic Performance

Analog Output Impedance

The output resistance, as in the case of the output capacitance, varies with the digital input code. This resistance,

looking back into the IOUT1 terminal, varies between 11 kW (the feedback resistor alone when all digital input are

LOW) and 7.5 kâ¦ (the feedback resistor in parallel with approximately 30 kâ¦ of the R-2R ladder network resistance

when any single bit logic is HIGH). Static accuracy and dynamic performance will be affected by these variations.

The gain and phase stability of the output amplifier, board layout, and power supply decoupling will all affect the

dynamic performance of the 8143. The use of a small compensation capacitor may be required when high speed

operational amplifierâs feedback resistor to provide the necessary phase compensation to critically damp the output.

The considerations when using high speed amplifiers are:

1. Phase compensation (see Figures 16 and 17).

2. Power supply decoupling at the device socket and use of proper grounding techniques.

Output Amplifier Considerations

When using high speed op amps, a small feedback capacitor (typically 5 pF-30 pF) should be used across the amplifi-

ers to minimize overshoot and ringing. For low speed or static applications, ac specification of the amplifier are not

very critical. In high speed applications, slew rate, settling time, open-loop gain and gain/phase margin specifications

of the amplifier should be selected for the desired performance. It has already been noted that an offset can be caused

by including the usual bias current compensation resistor in the amplifierâs noninverting input terminal. This resistor

should not be used. Instead, the amplifier should have a bias current that is low over the temperature range of interest.

Static accuracy is affected by the variation in the DACâs output resistance. This variation is best illustrated by using the

circuit of Figure 14 and the equation:

07.23.03 REV 3

All data sheets are subject to change without notice 12

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