UPD78F0411GA-GAM-AX Datasheet, PDF (312/564 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 12 10-BIT SUCCESSIVE APPROXIMATION TYPE A/D CONVERTER (μPD78F041x only)
Reference
voltage
input
Figure 12-20. Analog Input Pin Connection
If there is a possibility that noise equal to or higher than AVREF or
equal to or lower than AVSS may enter, clamp with a diode with a
small VF value (0.3 V or lower).
AVREF
C = 100 to 1,000 pF
ANI0 to ANI5
AVSS
VSS
(5) ANI0/SEG21/P20 to ANI5/SEG16/P25 pins
<1> The analog input pins (ANI0 to ANI5) are also used as I/O port pins (P20 to P25).
When A/D conversion is performed with any of ANI0 to ANI5 selected, do not access P20 to P25 while
conversion is in progress; otherwise the conversion resolution may be degraded. It is recommended to any
pin of P20 to P25 used as digital I/O port starting with the ANI0/P20 that is the furthest from AVREF.
<2> If a digital pulse is input or output, or segment-output to the pins adjacent to the pins currently used for A/D
conversion, the expected value of the A/D conversion may not be obtained due to coupling noise.
Therefore, do not input or output a pulse, or segment-output to the pins adjacent to the pin undergoing A/D
conversion.
(6) Input impedance of ANI0 to ANI5 pins
This A/D converter charges a sampling capacitor for sampling during sampling time.
Therefore, only a leakage current flows when sampling is not in progress, and a current that charges the
capacitor flows during sampling. Consequently, the input impedance fluctuates depending on whether sampling
is in progress, and on the other states.
To make sure that sampling is effective, however, it is recommended to keep the output impedance of the analog
input source to within 10 kΩ, and to connect a capacitor of about 100 pF to the ANI0 to ANI5 pins (see Figure 12-
20).
(7) AVREF pin input impedance
A series resistor string of several tens of kΩ is connected between the AVREF and AVSS pins.
Therefore, if the output impedance of the reference voltage source is high, this will result in a series connection to
the series resistor string between the AVREF and AVSS pins, resulting in a large reference voltage error.
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User’s Manual U18698EJ1V0UD