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Section 23 A/D Converter
23.7.3
Influences on Absolute Accuracy
Adding capacitance results in coupling with GND, and therefore noise in GND may adversely
affect the absolute accuracy. Be sure to make the connection to an electrically stable GND such as
AVss.
Care is also required to insure that filter circuits do not communicate with digital signals on the
mounting board, so acting as antennas.
23.7.4
Setting Range of Analog Power Supply and Other Pins
If conditions shown below are not met, the reliability of this LSI may be adversely affected.
•
Analog input voltage range
The voltage applied to analog input pin ANn during A/D conversion should be in the range
AVss ≤ V
≤ AVref.
AN
• Relation between AVcc, AVss and Vcc, Vss
The relationship between AVcc, AVss and Vcc, Vss should be Avcc = Vcc ± 0.3V and AVss =
Vss. When the A/D converter is not used, set AVcc = Vcc and Avss = Vss.
• AVref pin reference voltage specification range
The reference voltage of the AVref pin should be in the range AVref ≤ AVcc.
23.7.5
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), the analog reference
voltage (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.
Rev. 1.00 Mar. 12, 2008 Page 912 of 1178
REJ09B0403-0100
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