Toshiba TLCS-870/C1 Series, Manual

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Page 302
20. 10-bit AD Converter (ADC)
20.7 Precautions about the AD Converter
TMP89FM42
RA001
20.7 Precautions about the AD Converter
20.7.1 Analog input pin voltage range
Analog input pins (AIN0 through AIN7) should be used at voltages from VAREF to VSS. If any voltage out-
side this range is applied to one of the analog input pins, the converted value on that pin becomes uncertain,
and converted values on other pins will also be affected.
20.7.2 Analog input pins used as input/output ports
Analog input pins (AIN0 to AIN7) are also used as input/output ports. In using one of analog input pins
(ports) to execute AD conversion, input/output instructions at all other pins (ports) must not be executed. If
they are executed, there is the possibility that the accuracy of AD conversion may deteriorate. This also applies
to pins other than analog input pins; if one pin receives inputs or generates outputs, noise may occur and its
adjacent pins may be affected by that noise.
20.7.3 Noise countermeasure
The internal equivalent circuit of the analog input pins is shown in Figure 20-5. The higher the output imped-
ance of the analog input source, the more susceptible it becomes to noise. Therefore, make sure the output
impedance of the signal source in your design is 5 k
Ω
or less. It is recommended that a capacitor be attached
externally.
Figure 20-5 Analog Input Equivalent Circuit and Example of Input Pin Processing
DA converter
Analog comparator
rnal resistance:
rnal capacitance:
#!Undefined!# k
Ω
(typ)
DA converter
AINi
Analog comparator
Internal resistance:
Permissible signal
source impedance:
Internal capacitance:
5 k
Ω
(typ) 5 k
Ω
(max)
Note) i = 7 to 0
C = 22 pF (typ.)