TMP86C846NG Datasheet, PDF (145/160 Pages) Toshiba Semiconductor – 8 Bit Microcontroller

TMP86C846NG
12.6 Precautions about AD Converter
12.6.1 Analog input pin voltage range
Make sure the analog input pins (AIN0 to AIN7) are used at voltages within VAREF to AVSS. If any voltage
outside this range is applied to one of the analog input pins, the converted value on that pin becomes uncertain.
The other analog input pins also are affected by that.
12.6.2 Analog input shared pins
The analog input pins (AIN0 to AIN7) are shared with input/output ports. When using any of the analog
inputs to execute AD conversion, do not execute input/output instructions for all other ports. This is necessary
to prevent the accuracy of AD conversion from degrading. Not only these analog input shared pins, some other
pins may also be affected by noise arising from input/output to and from adjacent pins.
12.6.3 Noise Countermeasure
The internal equivalent circuit of the analog input pins is shown in Figure 12-5. The higher the output
impedance of the analog input source, more easily they are susceptible to noise. Therefore, make sure the out-
put impedance of the signal source in your design is 5 kΩ or less. Toshiba also recommends attaching a capac-
itor external to the chip.
AINi
Permissible signal
source impedance
5 kΩ (max)
Note) i = 7 to 0
Internal resistance
5 kΩ (typ)
Internal capacitance
C = 12 pF (typ.)
Analog comparator
DA converter
Figure 12-5 Analog Input Equivalent Circuit and Example of Input Pin Processing
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