Datasheet

Section 16 A/D Converter (8 Analog Input Channel Version)
Rev.6.00 Sep. 27, 2007 Page 721 of 1268
REJ09B0220-0600
FS
Offset error
Nonlinearity
error
Actual A/D conversion
characteristic
Analog
input voltage
Digital output
Ideal A/D conversion
characteristic
Full-scale error
Figure 16.9 A/D Conversion Precision Definitions (2)
Permissible Signal Source Impedance: The chip’s analog input is designed so that conversion
precision is guaranteed for an input signal for which the signal source impedance is 5 kΩ or less.
This specification is provided to enable the A/D converter's sample-and-hold circuit input
capacitance to be charged within the sampling time; if the sensor output impedance exceeds 5 kΩ,
charging may be insufficient and it may not be possible to guarantee the A/D conversion
precision.
If a large capacitance is provided externally, the input load will essentially comprise only the
internal input resistance of 10 kΩ, and the signal source impedance is ignored. However, since a
low-pass filter effect is obtained in this case, it may not be possible to follow an analog signal with
a large differential coefficient (e.g., 5 mV/µs or greater).
When converting a high-speed analog signal, a low-impedance buffer should be inserted.