SH7147 Datasheet, PDF (684/1108 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer SuperH™ RISC engine Family

Section 15 A/D Converter (ADC)
15.7 Usage Notes
15.7.1 Analog Input Voltage Range
The voltage applied to analog input pin (ANn) during A/D conversion should be in the range
AV_refl ≤ ANn (n = 0 to 15) ≤ AV_refh.
15.7.2 Relationship between AVcc, AVss and Vcc, Vss
When using the A/D converter, set AVcc = 5.0 V ±0.5 V and AVss = Vss. When the A/D
converter is not used, set AVss = Vss, and do not leave the AVcc pin open.
15.7.3 Range of AV_refh and AV_refl Pin Settings
When using the A/D converter, set AV_refh = 4.5 to AVcc. When the A/D converter is not used, set
AV_refh ≤ AVcc. If these conditions are not met, the reliability of the LSI may be adversely affected.
For AV_refl, set AV_refl = AVss = Vss.
15.7.4 Notes on Board Design
In board design, digital circuitry and analog circuitry should be as mutually isolated as possible,
and the layout in which the digital circuit signal lines and analog circuit signal lines cross or are in
close proximity to each other should be avoided as much as possible. Failure to do so may result in
the incorrect operation of the analog circuitry due to inductance, adversely affecting the A/D
conversion values.
Also, digital circuitry must be isolated from the analog input signals (AN0 to AN15), analog
reference power supply (AV_refh and AV_refl), the analog power supply (AVcc), and the analog ground
(AVss). Also, AVss should be connected at one point to a stable digital ground (Vss) on the board.
15.7.5 Notes on Noise Countermeasures
To prevent damage due to an abnormal voltage, such as an excessive surge at the analog input pins
(AN0 to AN15) and analog reference power supply (AV_refh, AV_refl), a protection circuit should be
connected between the AVcc and AVss, as shown in figure 15.9. Also, the bypass capacitors
connected to AV_refh and AV_refl and the filter capacitor connected to ANn should be connected to the
AVss. If a filter capacitor is connected as shown in figure 15.9, the input currents at the analog
input pin (ANn) are averaged, and an error may occur. Careful consideration is therefore required
when deciding the circuit constants.
Rev. 3.00 Oct. 06, 2008 Page 660 of 1080
REJ09B0230-0300