183
CHAPTER 11 A/D CONVERTER
Preliminary User’s Manual U13420EJ2V0UM00
(4) Noise countermeasures
To maintain the 8-bit resolution, attention must be paid to noise input to pin AV
REF
and pins ANI0 to ANI7. Because
the effect increases in proportion to the output impedance of the analog input source, it is recommended that
a capacitor be connected externally as shown in Figure 11-8 to reduce noise.
Figure 11-8. Analog Input Pin Connection
(5) ANI0 to ANI7
If digital pulses are applied to a pin adjacent to the pin in the process of A/D conversion, the expected A/D
conversion value may not be obtainable due to coupling noise. Therefore, avoid applying pulses to pins adjacent
to the pin undergoing A/D conversion.
(6) AV
REF
pin input impedance
A series resistor string of approx. 10 k
Ω
is connected between the AV
REF
pin and the AV
SS
pin.
Therefore, when the output impedance of the reference voltage is too high, it seems as if the AV
REF
pin and the
series resistor string are connected in parallel. This may cause a greater reference voltage error.
Reference
voltage
input
C = 100 to 1000 pF
If there is a possibility that noise equal to or higher than AV
REF
or
equal to or lower than AV
SS
may enter, clamp with a diode with a
small V
F
value (0.3 V or lower).
AV
REF
V
DD0
AV
SS
V
SS0
ANI0 to ANI7
Summary of Contents for mPD780065 Series
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