ADC08061 datasheet(14/16 Pages) NSC

14 / 16 page

Application Information (Continued)

The ADC08061 can perform accurate conversions of

full-scale input signals at frequencies from dc to more than

300 kHz (full power bandwidth) without the need of an exter-

nal sample-and-hold (S/H).

7.0 LAYOUT, GROUNDS, AND BYPASSING

In order to ensure fast, accurate conversions from the

ADC08061/2, it is necessary to use appropriate circuit board

layout techniques. Ideally, the analog-to-digital converter’s

ground reference should be low impedance and free of noise

from other parts of the system. Digital circuits can produce a

great deal of noise on their ground returns and, therefore,

should have their own separate ground lines. Best perfor-

mance is obtained using separate ground planes for the digi-

tal and analog parts of the system.

The analog inputs should be isolated from noisy signal

traces to avoid having spurious signals couple to the input.

Any external component (e.g., an input filter capacitor) con-

nected across the inputs should be returned to a very clean

ground point. Incorrectly grounding the ADC08061/2 will re-

sult in reduced conversion accuracy.

The V

+ supply pin, V

REF+, and VREF− (if not grounded)

should be bypassed with a parallel combination of a 0.1 µF

ceramic capacitor and a 10 µF tantalum capacitor placed as

close as possible to the supply pin using short circuit board

traces. See

Figures 8, 9.

External Reference 2.5V Full-Scale

(Standard Application)

DS011086-20

Note : Bypass capacitors consist of a 0.1 µF

ceramic in parallel with a 10 µF bead tantalum.

Power Supply as Reference

DS011086-21

Input Not Referred to GND

DS011086-22

* Signal source driving VIN(−) must be capable

of sinking 5 mA.

FIGURE 8. Analog Input Options

DS011086-23

Note the multiple bypass capacitors on the reference and power supply pins. VREF− should be bypass to analog ground using multiple capacitors if it is not

grounded (see Section 7.0 “Layout, Grounds, and Bypassing”). VIN1 is shown with an optional input protection network.

FIGURE 9. Typical Connection

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