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14.7.3
Influences on Absolute Accuracy
Adding capacitance results in coupling with GND, and therefore noise in GND may adversely
affect 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, acting as antennas.
14.7.4
Setting Range of Analog Power Supply and Other Pins
If the conditions shown below are not met, the reliability of the 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
≤ Vref.
AN
• Relation between AVcc, AVss and Vcc, Vss
As the relationship between AVcc, AVss and Vcc, Vss, set AVcc = Vcc ± 0.3 V and AVss =
Vss. If the A/D converter is not used, set AVcc = Vcc and AVss = Vss.
• Vref setting range
The reference voltage at the Vref pin should be set in the range Vref ≤ AVcc.
14.7.5
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.
Digital circuitry must be isolated from the analog input pins (AN0 to AN7), analog reference
power supply (Vref), and analog power supply (AVcc) by the analog ground (AVss). Also, the
analog ground (AVss) should be connected at one point to a stable ground (Vss) on the board.
Section 14 A/D Converter
Rev.2.00 Jun. 28, 2007 Page 541 of 666
REJ09B0311-0200
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