H8S-2350 RENESAS [Renesas Technology Corp], H8S-2350 Datasheet - Page 692

• Manufacturer Part Number: H8S-2350
• Description: 16-Bit Single-Chip Microcomputer
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 15 A/D Converter
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
) by the analog ground (AV
).
ref
CC
SS
Also, the analog ground (AV
) should be connected at one point to a stable digital ground (V
)
SS
SS
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
) should be
ref
connected between AV
and AV
as shown in figure 15.7.
CC
SS
Also, the bypass capacitors connected to AV
and V
and the filter capacitor connected to AN0
CC
ref
to AN7 must be connected to AV
.
SS
If a filter capacitor is connected as shown in figure 15.7, 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
), an error will arise in the analog input pin voltage. Careful consideration is therefore required
in
when deciding the circuit constants.
Rev. 3.00 Sep 15, 2006 page 658 of 988
REJ09B0330-0300