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R01UH0336EJ0102 Rev.1.02
Page 1346 of 1538
Jul 17, 2014
V850E2/PG4-L
Section 23 A/D Converter
(2)
Wiring of Power Supply
To minimize the influence on the A/D converter accuracy due to the factors
such as switching noise on the digital circuit, the following measures are
recommended.
(a) Use one full side of the board for the power-supply wiring or connect the
wiring in as large a grid pattern as possible.
(b) Insert a bypass capacitor in the vicinity of the pin lead between power
supply pins (EV
DD
, OSCV
DD
, V
DD
, AV
DDn
) and ground pins (EV
SS
,
OSCV
SS
, V
SS
, AV
SSn
). It is recommended to use approximately 0.1-
F
(reference value) multilayer ceramic capacitors or 4.7-
μ
F (reference value)
or greater tantalum electrolytic capacitors.
(c) We recommend isolating the analog power supply (AV
DDn
) from the digital
power supply (EV
DD
, OSCV
DD
, V
DD
) and supplying power via a series-
connected regulator. When a common power supply is to be used, connect
the analog power-supply line, digital power-supply line, and an electrolytic
capacitor at a point in the source of the supply but wire the power supplies
in isolation from each other on the board.
Insert a chip inductor at the point of entry for the analog power supply
voltage. In addition, earth the analog ground, digital ground, and an
electrolytic capacitor at a point in the source of the power supply, but wire
them in isolation from each other on the board.
(3)
Analog Reference Voltage Input Pins (AV
REFnP
, AV
REFnM
)
Insert a bypass capacitor between the leads of the AV
REFnP
pin and the
AV
REFnM
pin as close as possible to the leads. It is recommended to use
approximately 0.1-
F (reference value) multilayer ceramic capacitors or 4.7-
F (reference value) or greater tantalum electrolytic capacitors.
(4)
Variation in A/D Conversion Results
A/D conversion results may vary according to the factors such as fluctuation of
the power supply voltage and noise. Erroneous conversion results may also be
produced if noise is generated on the analog input pin (ADCAnIm) and
reference voltage input pins (AV
REFnP
, AV
REFnM
).
To prevent the system from being affected by such variation and erroneous
conversion results, reduce them through software.
The following gives examples of using software to prevent bad influence.
• Perform A/D conversion multiple times and use the average value of the
results.
• If A/D conversion is continuously performed multiple times and any singular
conversion result is obtained, exclude it and use other results.
• If any obtained A/D conversion result is judged to be caused by a system
error, do not handle the error immediately; first check to see that the
erroneous result is caused again and then handle the error.