Precautions About Ad Converter; Analog Input Pin Voltage Range; Analog Input Shared Pins; Noise Countermeasure - Toshiba TLCS-870/C Series Manual

13.6 Precautions about AD Converter

13.6.1 Analog input pin voltage range

Make sure the analog input pins (AIN0 to AIN7) are used at voltages within VAREF to VSS. 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.

13.6.2 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.

13.6.3 Noise Countermeasure

The internal equivalent circuit of the analog input pins is shown in Figure 13-5. 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.
Permissible signal
source impedance
5 kΩ (max)
Note) i = 7 to 0
Figure 13-5 Analog Input Equivalent Circuit and Example of Input Pin Processing
Internal resistance
5 kΩ (typ)
AINi
Internal capacitance
C = 22 pF (typ.)
Page 149
TMP86PM29BUG
Analog comparator
DA converter