Rainbow-electronics ADC12041 Manual do Utilizador descarregar pdf (Página 27)

Analog Application Information (Continued)

TL/H/12441–45

FIGURE 10. Top View of Printed Circuit Board for a 28-Pin PLCC ADC12041

When measuring AC input signals, any crosstalk between

analog input lines and the reference lines (ADCIN

REF

) should be minimized. Crosstalk is minimized by re-

ducing any stray capacitance between the lines. This can be

done by increasing the clearance between traces, keeping

the traces as short as possible, shielding traces from each

other by placing them on different sides of the AGND plane,

or running AGND traces between them.

Figure 10

also shows the reference input bypass capacitors.

Here the reference inputs are considered to be differential.

The performance improves by having a 0.1 m F capacitor

between the V

REF

and V

REF

, and by bypassing in a

manner similar to that described for the supply pins. When a

single ended reference is used, V

REF

is connected to

AGND and only two capacitors are used between V

REF

and V

REF

(0.1 mF

10 mF). It is recommended to directly

connect the AGND side of these capacitors to the V

REF

instead of connecting V

REF

and the ground sides of the

capacitors separately to the ground planes. This provides a

significantly lower-impedance connection when using sur-

face mount technology.

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