tmp88ch40img TOSHIBA Semiconductor CORPORATION, tmp88ch40img Datasheet - Page 137

• Manufacturer Part Number: tmp88ch40img
• Description: 8 Bit Microcontroller
• Manufacturer: TOSHIBA Semiconductor CORPORATION

14.5 Precautions about AD Converter
14.5.1 Analog input pin voltage range
14.5.2 Analog input shared pins
14.5.3 Noise Countermeasure
Figure 14-5
Permissible signal
source impedance
5 kΩ (max)
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.
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.
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.
Make sure the analog input pins (AIN0 to AIN3) are used at voltages within VAREF to AVSS. If any voltage
The analog input pins (AIN0 to AIN3) are shared with input/output ports. When using any of the analog
The internal equivalent circuit of the analog input pins is shown in Figure 14-5. The higher the output
Note) i = 3 to 0
Analog Input Equivalent Circuit and Example of Input Pin Processing
AINi
Internal resistance
5 kΩ (typ)
Internal capacitance
Page 129
C = 22 pF (typ.)
Analog comparator
DA converter
TMP88CH40IMG