HD6417750RF240V Datasheet, PDF (485/606 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer H8S Family/H8S/2600 Series

Section 16 A/D Converter
16.7.4 Range of Analog Power Supply and Other Pin Settings
If the conditions below are not met, the reliability of the device 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_AN ≤ AVcc.
• Relationship between AVcc, AVss and Vcc, Vss
Set AVss = Vss as the relationship between AVcc, AVss and Vcc, Vss. If the A/D converter is
not used, the AVcc and AVss pins must not be left open.
16.7.5 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 AN11), 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.
16.7.6 Notes on Noise Countermeasures
A protection circuit should be connected in order to prevent damage due to abnormal voltage, such
as an excessive surge at the analog input pins (AN0 to AN11), between AVcc and AVss, as shown
in figure 16.7. Also, the bypass capacitors connected to AVcc and the filter capacitor connected to
AN0 to AN11 must be connected to AVss.
If a filter capacitor is connected, the input currents at the analog input pins (AN0 to AN11) 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 sample-and-hold circuit
in the A/D converter exceeds the current input via the input impedance (R_in), an error will arise in
the analog input pin voltage. Careful consideration is therefore required when deciding circuit
constants.
Rev. 7.00 Sep. 11, 2009 Page 449 of 566
REJ09B0211-0700