HD64F3048VTF8 Datasheet, PDF (585/903 Pages) Renesas Technology Corp – Hardware Manual Renesas 8-Bit Single-Chip

Section 15 A/D Converter
5. Note on Noise: To prevent damage from surges and other abnormal voltages at the analog
input pins (AN₀ to AN₇) and analog reference voltage pin (V_REF), connect a protection circuit
like the one in figure 15.7 between AV_CC and AV_SS. The bypass capacitors connected to AV_CC
and V_REF and the filter capacitors connected to AN₀ to AN₇ must be connected to AV_SS. If filter
capacitors like the ones in figure 15.7 are connected, the voltage values input to the analog
input pins (AN₀ to AN₇) will be smoothed, which may give rise to error. Error can also occur if
A/D conversion is frequently performed in scan mode so that the current that charges and
discharges the capacitor in the sample-and-hold circuit of the A/D converter becomes greater
than that input to the analog input pins via input impedance R_in. The circuit constants should
therefore be selected carefully.
*1
*1
R_in^*2
100 Ω
0.1 µF
Notes: 1. Numeric values are approximate.
10 µF
0.01 µF
AV_CC
V_REF
AN₀ to AN₇
AV_SS
2. R_in: input impedance
Figure 15.7 Example of Analog Input Protection Circuit
Rev. 3.00 Sep 27, 2006 page 557 of 872
REJ09B0325-0300