Chapter 14
A/D Converter
XIV - 44 Operation
14.3.3 Cautions
A/D converter can be damaged by noise easily; therefore, anti-noise measures should be taken adequately.
The following shows cautions for anti-noise measures and the recommended circuit when A/D converter is used.
■ Anti-noise Measures
To A/D input (analog input pin ADINn), add condenser near the VSS pins of micro controller.
Figure:14.3.10 A/D Converter Recommended Example
■ Recommended Circuit
For high precision of A/D conversion, the following cautions on A/D converter should be kept.
1. The input impedance R of A/D input pin should be under 500 kΩ, *1 and the external capacitor C which is
more than 1000 pF, under 1 µF *1 should be connected to it.
2. The A/D conversion frequency should be set in regard to R, C.
3. At the A/D conversion, if the output level of microcontroller is changed, or the peripheral added circuit is
switched to ON/OFF, the A/D conversion could work wrongly, as the analog input pins and power pins can not
be fixed. At the setup checking confirm the waveform of analog input pins.
Figure:14.3.11 Recommended Circuit
VDD
Chip Power
ADIN00
ADIN15
V
SS
VDD
VSS
VDD
VSS
12
10
1 mF C 1000 pF
*1
but, R 500 kΩ
microcontroller
R
C
Vss
A/D Input pin
*1 is a reference value.
Equivalent circuit block that
outputs analog signal
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