HD64F2149 Datasheet, PDF (680/1035 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

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 AVSS ≤ 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 AVSS ≤ CINn ≤
AVref and VSS ≤ CINn ≤ VCC (n = 0 to 15).
3. Relation between AVCC, AVSS and VCC, VSS
As the relationship between AVCC, 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 AVref ≤ 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.
Also, the bypass capacitors connected to AVCC, AVref and the filter capacitor connected to AN0
to AN7 must be connected to AVSS.
If a filter capacitor is connected as shown in figure 20.7, the input currents at the analog input pins
(AN0 to AN7) are averaged, and so an error may arise. Also, when A/D conversion is performed
frequently, as in scan mode, if the current charged and discharged by the capacitance of the
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