SH7046 Datasheet, PDF (429/611 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7046 Series

Section 13 A/D Converter
13.7.4 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 ≤ VAN ≤ AVcc.
• Relationship between AVcc, AVss and Vcc, Vss
Set AVss = Vss for 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.
13.7.5 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 (AN8 to AN19), 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.
13.7.6 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 (AN8 to AN19), between AVcc and AVss, as shown
in figure 13.7. Also, the bypass capacitors connected to AVcc and the filter capacitor connected to
AN8 to AN19 must be connected to AVss.
If a filter capacitor is connected, the input currents at the analog input pins (AN8 to AN19) 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. 4.00 Dec 05, 2005 page 385 of 564
REJ09B0270-0400