541
Chapter 15
A/D Converter
Preliminary User’s Manual U15839EE1V0UM00
15.6 A/D Converter Precautions
(1)
Current consumption in standby mode
A/D converter current consumption can be reduced by stopping the A/D conversion operation. A/D
conversion operation is stopped by resetting the ADCS bit of the A/D converter mode register
ADM to (0).
(2)
Input range of ANI0 to ANI11
Keep the input voltage of the ANI0 through ANI11 pins to within the rated range. If a input voltage
greater than AV
DD
or lower than AV
SS
(even within the range of the absolute maximum ratings) is
input to a channel, the converted value of the channel becomes undefined. Moreover, the values
of the other channels may also be affected.
(3)
Noise counter measures
To maintain 10-bit resolution, attention must be paid to noise input to pin AV
DD
and pins ANI0 to
ANI11. 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 15-13,
“Analog Input Pin Handling,” on page 541 to reduce noise.
Figure 15-13:
Analog Input Pin Handling
(4)
ANI0 to ANI11
The analog input pins (ANI0 to ANI11) also function as input port pins (P80 to P83, P70 to P77).
When A/D conversion is performed with any of pins ANI0 to ANI11 selected, do not execute a port
input instruction while conversion is in progress, as this may reduce the conversion resolution.
Also, 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.
Reference
voltage
input
C = 100 to 1000 pF
If there is a possibility that noise equal to or higher than AV
DD
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
DD
AV
SS
V
SS
ANI0 to ANI7
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