DAC128S085EB/NOPB National Semiconductor, DAC128S085EB/NOPB Datasheet - Page 21

• Manufacturer Part Number: DAC128S085EB/NOPB
• Description: BOARD EVALUATION FOR DAC128S085
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of DAC128S085EB/NOPB

• Number Of Dac's: 8
• Number Of Bits: 12
• Outputs And Type: 8, Single Ended
• Data Interface: Serial
• Settling Time: 6µs
• Dac Type: Voltage
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 105°C
• Utilized Ic / Part: DAC128S085
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: DAC128S085EB

2.7 LAYOUT, GROUNDING, AND BYPASSING
For best accuracy and minimum noise, the printed circuit
board containing the DAC128S085 should have separate
analog and digital areas. The areas are defined by the loca-
tions of the analog and digital power planes. Both of these
planes should be located in the same board layer. 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 DAC128S085. Special care
is required to guarantee that digital signals with fast edge
rates do not pass over split ground planes. They must always
have a continuous return path below their traces.
For best performance, the DAC128S085 power supply should
be bypassed with at least a 1µF and a 0.1µF capacitor. The
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0.1µF capacitor needs to be placed right at the device supply
pin. The 1µF or larger valued capacitor can be a tantalum
capacitor while the 0.1µF capacitor needs to be a ceramic
capacitor with low ESL and low ESR. If a ceramic capacitor
with low ESL and low ESR is used for the 1µF value and it
can be placed right at the supply pin, the 0.1µF capacitor can
be eliminated. Capacitors of this nature typically span the
same frequency spectrum as the 0.1µF capacitor and thus
eliminate the need for the extra capacitor. The power supply
for the DAC128S085 should only be used for analog circuits.
It is also advisable to avoid the crossover of analog and digital
signals. This helps minimize the amount of noise from the
transitions of the digital signals from coupling onto the sensi-
tive analog signals such as the reference pins and the DAC
outputs.
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