Table of Contents
Advertisement
14.6
Usage Notes
The following points should be noted when using the A/D converter.
Setting Range of Analog Power Supply and Other Pins
1. Analog input voltage range
The voltage applied to analog input pins ANn during A/D conversion should be in the range
≤ ANn ≤ V
AV
SS
ref
2. Relation between AV
As the relationship between AV
is not used, the AV
3. V
input range
ref
The analog reference voltage input at the V
V
pin should be set as V
ref
pin open.
If conditions 1, 2, and 3 above are not met, the reliability of the device may be adversely affected.
Notes on Board Design: In board design, digital circuitry and analog circuitry should be as
mutually isolated as possible, and layout in which digital circuit signal lines and analog circuit
signal lines cross or are in close proximity should be avoided as far as possible. Failure to do so
may result in incorrect operation of the analog circuitry due to inductance, adversely affecting A/D
conversion values.
Also, digital circuitry must be isolated from the analog input signals (AN0 to AN7), analog
reference power supply (V
Also, the analog ground (AV
on the board.
Notes on Noise Countermeasures: A protection circuit connected to prevent damage due to an
abnormal voltage such as an excessive surge at the analog input pins (AN0 to AN7) and analog
reference power supply (V
14-7.
Also, the bypass capacitors connected to AV
to AN7 must be connected to AV
If a filter capacitor is connected as shown in figure 14-7, the input currents at the analog input pins
(AN0 to AN7) are averaged, and so an error may arise. Also, when A/D conversion is performed
frequently, as in scan mode, if the current charged and discharged by the capacitance of the
sample-and-hold circuit in the A/D converter exceeds the current input via the input impedance
Rev. 5.00, 12/03, page 534 of 1088
.
, AV
and V
, V
CC
SS
CC
, AV
CC
SS
and AV
pins must not be left open.
CC
SS
= V
when the A/D converter is not used. Do not leave the V
ref
CC
), and analog power supply (AV
ref
) should be connected at one point to a stable digital ground (V
SS
) should be connected between AV
ref
.
SS
SS
and V
, V
, set AV
CC
SS
pin should be set in the range V
ref
) by the analog ground (AV
CC
CC
and V
and the filter capacitor connected to AN0
CC
ref
= V
. If the A/D converter
SS
SS
≤ AV
ref
and AV
as shown in figure
SS
. The
CC
ref
).
SS
)
SS
Advertisement
Table of Contents
