adc101c027cimkx National Semiconductor Corporation, adc101c027cimkx Datasheet - Page 30

• Manufacturer Part Number: adc101c027cimkx
• Description: I2c-compatible, 12-bit Analog-to-digital Converter Adc With Alert Function
• Manufacturer: National Semiconductor Corporation

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2.4 LAYOUT, GROUNDING, AND BYPASSING
For best accuracy and minimum noise, the printed circuit
board containing the ADC101C021 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 on the same board layer. There
should be a single ground plane. A single, solid 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 ana-
log and digital ground currents. Separate ground planes
should only be utilized when the fencing technique is inade-
quate. The separate ground planes must be connected in one
place, preferably near the ADC101C021. Special care is re-
30
quired to guarantee that signals do not pass over power plane
boundaries. They must always have a continuous return path
below their traces.
The ADC101C021 power supply should be bypassed with a
4.7µF and a 0.1µF capacitor as close as possible to the device
with the 0.1µF right at the device supply pin. The 4.7µF ca-
pacitor should be a tantalum type and the 0.1µF capacitor
should be a low ESL type. The power supply for the
ADC101C021 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.