4.0 Inherent Sample-and-Hold

(Continued)

The ADC1061 can perform accurate conversions of input

signals at frequencies from DC to greater than 160 kHz with-

out the need for external sampling circuitry.

5.0 Power Supply Considerations

The ADC1061 is designed to operate from a +5V (nominal)

power supply. There are two supply pins, AV

These pins allow separate external bypass capacitors for the

analog and digital portions of the circuit. To guarantee accu-

rate conversions, the two supply pins should be connected

to the same voltage source, and each should be bypassed

with a 0.1 µF ceramic capacitor in parallel with a 10 µF tan-

talum capacitor. Depending on the circuit board layout and

other system considerations, more bypassing may be neces-

sary.

It is important to ensure that none of the ADC1061’s input or

output pins are ever driven to a voltage more than 300 mV

above AV

these voltage limits are exceeded, the overdrive current into

or out of any pin on the ADC1061 must be limited to less

than 5 mA, and no more than 20 mA of overdrive current (all

overdriven pins combined) should flow. In systems with mul-

tiple power supplies, this may require careful attention to

power supply sequencing. The ADC1061’s power supply

pins should be at the proper voltage before signals are ap-

plied to any of the other pins.

6.0 Layout and Grounding

In order to ensure fast, accurate conversions from the

ADC1061, it is necessary to use appropriate circuit board

layout techniques. The analog ground return path should be

low-impedance and free of noise from other parts of the sys-

tem. Noise from digital circuitry can be especially trouble-

some, so digital grounds should always be separate from

analog grounds. For best performance, separate ground

planes should be provided for the digital and analog parts of

the system.

All bypass capacitors should be located as close to the con-

verter as possible and should connect to the converter and

to ground with short traces. The analog input should be iso-

lated from noisy signal traces to avoid having spurious sig-

nals couple to the input. Any external component (e.g., a fil-

ter capacitor) connected across the converter’s input should

be connected to a very clean ground return point. Grounding

the component at the wrong point will result in reduced con-

version accuracy.

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