adc1204802 National Semiconductor Corporation, adc1204802 Datasheet - Page 30

• Manufacturer Part Number: adc1204802
• Description: 12-bit Plus Sign 216khz 8-channel Sampling Analog-to-digital Converter
• Manufacturer: National Semiconductor Corporation

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Analog Application Information
When measuring AC input signals, any crosstalk between
analog input/output lines and the reference lines (CH0–CH7,
MUXOUT
Crosstalk is minimized by reducing any stray capacitance
between the lines. This can be done by increasing the clear-
ance between traces, keeping the traces as short as pos-
sible, shielding traces from each other by placing them on
different sides of the AGND plane, or running AGND traces
between them.
Figure 21 also shows the reference input bypass capacitors.
Here the reference inputs are considered to be differential.
±
, ADC IN
±
FIGURE 21. Top View of Printed Circuit Board for a 44-Pin PLCC ADC12048
, V
REF
±
) should be minimized.
(Continued)
30
The performance improves by having a 0.1 µF capacitor
between the V
ner similar to that described for the supply pins. When a
single ended reference is used, V
AGND and only two capacitors are used between V
V
connect the AGND side of these capacitors to the V
instead of connecting V
capacitors separately to the ground planes. This provides a
significantly lower-impedance connection when using sur-
face mount technology.
REF
− (0.1 µF + 10 µF). It is recommended to directly
REF
+ and V
REF
REF
− and the ground sides of the
−, and by bypassing in a man-
REF
− is connected to
REF
01238738
+ and
REF
−