Rev. 2.00, 09/03, page 539 of 690
•
Relationships of AV
CC
, AV
SS
and V
CC
Q, V
SS
Q: AV
CC
= V
CC
Q ± 0.2 V and AV
SS
= V
SS
Q. 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.
0.01
µ
F
10
µ
F
AV
CC
AN0 to AN3
AV
SS
This LSI
*
1
100
Ω
0.1
µ
F
Notes: 1. Values are for reference.
R
in
*
2
2. R
in
is input impedance.
Figure 21.6 Example of Analog Input Protection Circuit
Summary of Contents for SH7705
Page 2: ......
Page 70: ...Rev 2 00 09 03 page 24 of 690 ...
Page 194: ...Rev 2 00 09 03 page 148 of 690 ...
Page 284: ...Rev 2 00 09 03 page 238 of 690 ...
Page 338: ...Rev 2 00 09 03 page 292 of 690 ...
Page 354: ...Rev 2 00 09 03 page 308 of 690 ...
Page 374: ...Rev 2 00 09 03 page 328 of 690 ...
Page 420: ...Rev 2 00 09 03 page 374 of 690 ...
Page 476: ...Rev 2 00 09 03 page 430 of 690 ...
Page 482: ...Rev 2 00 09 03 page 436 of 690 ...
Page 552: ...Rev 2 00 09 03 page 506 of 690 ...
Page 630: ...Rev 2 00 09 03 page 584 of 690 ...
Page 739: ...SH7705 Group Hardware Manual REJ09B0082 0200O ...