HD6413008VF25 Datasheet, PDF (474/688 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

14. A/D Converter
14.6 Usage Notes
When using the A/D converter, note the following points:
1. Analog Input Voltage Range
During A/D conversion, the voltages input to the analog input pins AN_n should be in the range
AV_SS ≤ AN_n ≤ V_REF.
2. Relationships of AV_CC and AV_SS to V_CC and V_SS
AV_CC, AV_SS, V_CC, and V_SS should be related as follows: AV_SS = V_SS. AV_CC and AV_SS must not be
left open, even if the A/D converter is not used.
3. V_REF Programming Range
The reference voltage input at the V_REF pin should be in the range V_REF ≤ AV_CC.
4. Note on Board Design
In board layout, separate the digital circuits from the analog circuits as much as possible.
Particularly avoid layouts in which the signal lines of digital circuits cross or closely approach
the signal lines of analog circuits. Induction and other effects may cause the analog circuits to
operate incorrectly, or may adversely affect the accuracy of A/D conversion.
The analog input signals (AN₀ to AN₇), analog reference voltage (V_REF), and analog supply
voltage (AV_CC) must be separated from digital circuits by the analog ground (AV_SS). The
analog ground (AV_SS) should be connected to a stable digital ground (V_SS) at one point on the
board.
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
14.7 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 14.7 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.
Rev.4.00 Aug. 20, 2007 Page 428 of 638
REJ09B0395-0400