HD6417705F133V Datasheet, PDF (587/741 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

• Relationships of AV_CC, AV_SS and V_CCQ, V_SSQ: AV_CC = V_CCQ ± 0.2 V and AV_SS = V_SSQ. Even
when the A/D converter is not used, do not open AV_CC and AV_SS.
21.7.4 Notes on Board Design
In designing a board, separate digital circuits and analog circuits. Do not intersect or locate closely
signal lines of a digital circuit and an analog circuit. An analog circuit may malfunction due to
induction, thus affecting A/D conversion values. Separate analog input pins (AN0 to AN3) and the
analog power voltage (AVcc) from digital circuits with analog ground (AVss). Connect analog
ground (AVss) to one point of stable ground (Vss) on the board.
21.7.5 Notes on Countermeasures to Noise
Connect a protective circuit between AVcc and AVss, as shown in figure 21.6, to prevent damage
of analog input pins (AN0 to AN3) due to abnormal voltage such as excessive serge. Connect a
bypass capacitor that is connected to AVcc and a capacitor for a filter that is connected to AN0 to
AN3 to AVss.
When a capacitor for a filter is connected, input currents of AN0 to AN3 are averaged, may
causing errors. If A/D conversion is frequently performed in scan mode, voltages of analog input
pins cause errors when a current that is charged/discharged for capacitance of a sample & hold
circuit in the A/D converter is higher than a current that is input through input impedance (Rin).
Therefore, determine a circuit constant carefully.
R_in^*2
100 Ω
*1
0.1 µF
Notes: 1. Values are for reference.
10 µF
0.01 µF
AVCC
AN0 to AN3
This LSI
AVSS
2. R_in is input impedance.
Figure 21.6 Example of Analog Input Protection Circuit
Rev. 2.00, 09/03, page 539 of 690