TMP86P203PG Datasheet, PDF (87/108 Pages) Toshiba Semiconductor – 8 Bit Microcontroller

TMP86P203PG
9.4 Precautions about AD Converter
9.4.1 Analog input pin voltage range
Make sure the analog input pins (AIN2 to AIN5) are used at voltages within VSS below VDD. 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.
9.4.2 Analog input shared pins
The analog input pins (AIN2 to AIN5) 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.
9.4.3 Noise countermeasure
The internal equivalent circuit of the analog input pins is shown in Figure 9-4. The higher the output imped-
ance of the analog input source, more easily they are susceptible to noise. Therefore, make sure the output
impedance of the signal source in your design is 5 kΩ or less. Toshiba also recommends attaching a capacitor
external to the chip.
Allowable signal
source impedance
5 kΩ (max)
Note) i = 5 to 2
AIN i
Internal resistance
5 kΩ (typ)
Internal capacitance
C = 22 pF (typ.)
Analog comparator

DA converter
Figure 9-4 Analog Input Equivalent Circuit and Example of Input Pin Processing
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