HD6433044 Datasheet, PDF (550/867 Pages) Hitachi Semiconductor – Hitachi Single-Chip Microcomputer

6. 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 Rin. The circuit
constants should therefore be selected carefully.
*1
*1
Rin^*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. Rin: input impedance
Figure 15-7 Example of Analog Input Protection Circuit
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