HD6432142 datasheet(674/1177 Pages) RENESAS

674 / 1177 page

Section 20 A/D Converter

Rev. 4.00 Sep 27, 2006 page 630 of 1130

REJ09B0327-0400

20.6

Usage Notes

The following points should be noted when using the A/D converter.

Setting Range of Analog Power Supply and Other Pins

1. Analog input voltage range

The voltage applied to the ANn analog input pins during A/D conversion should be in the

range AV

SS ≤ ANn ≤ AVref (n = 0 to 7).

2. Digital input voltage range

The voltage applied to the CINn digital input pins should be in the range AV

SS ≤ CINn ≤ AVref

and V

SS ≤ CINn ≤ VCC (n = 0 to 15).

3. Relation between AV

CC, AVSS and VCC, VSS

As the relationship between AV

CC, AVSS and VCC, VSS, set AVSS = VSS. If the A/D converter is

not used, the AVCC and AVSS pins must on no account be left open.

4. Setting Range of AVref Pin:

The reference voltage supplied via the AVref pin should be in the range AV

ref ≤ AVCC.

If conditions 1 to 4 above are not met, the reliability of the device may be adversely affected.

Notes on Board Design

In board design, digital circuitry and analog circuitry should be as mutually isolated as possible,

and layout in which digital circuit signal lines and analog circuit signal lines cross or are in close

proximity should be avoided as far as possible. Failure to do so may result in incorrect operation

of the analog circuitry due to inductance, adversely affecting A/D conversion values.

Also, digital circuitry must be isolated from the analog input signals (AN0 to AN7), analog

reference power supply (AVref), and analog power supply (AVCC) by the analog ground (AVSS).

Also, the analog ground (AVSS) should be connected at one point to a stable digital ground (VSS)

on the board.

Notes on Noise Countermeasures

A protection circuit connected to prevent damage due to an abnormal voltage such as an excessive

surge at the analog input pins (AN0 to AN7) or analog reference power supply pin (AVref) should

be connected between AVCC and AVSS as shown in figure 20.7.

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