Usage Notes - Renesas H8S Series Hardware Manual

16.6

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 AN0 to AN7 during A/D conversion should be in the range AV
V .
ref
(2) Relation between AV
As the relationship between AV
AV pins must on no account be left open.
SS
(3) V input range
ref
The analog reference voltage input at the V
Note: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
and analog power supply (AV
one point to a stable digital ground (V
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
between AV and AV
CC SS
Also, the bypass capacitors connected to AV
connected to AV .
SS
If a filter capacitor is connected as shown in figure 16-7, 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 (R
required when deciding the circuit constants.
, AV and V , V
CC SS CC SS
, AV and V
CC SS
ref
) by the analog ground (AV
CC
) on the board.
SS
as shown in figure 16-7.
and V
CC
), an error will arise in the analog input pin voltage. Careful consideration is therefore
in
, V , set AV = V
CC SS SS SS
pin set in the range V
ref
). Also, the analog ground (AV
SS
and the filter capacitor connected to AN0 to AN7 must be
ref
. If the A/D converter is not used, the AV
≤ AV
.
CC
) should be connected at
SS
ref
Rev.6.00 Oct.28.2004 page 551 of 1016
≤ ANn ≤
SS
and
CC
),
ref
) should be connected
REJ09B0138-0600H