SH7205 Datasheet, PDF (1089/1904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7200 Series

AN0 to AN7
3 kΩ
20 pF
Section 21 A/D Converter (ADC)
To A/D converter
Note: Values are reference values.
Figure 21.9 Analog Input Pin Equivalent Circuit
Table 21.7 Analog Input Pin Ratings
Item
Min.
Max.
Unit
Analog input capacitance

20
pF
Allowable signal-source impedance

5
kΩ
21.7.5 Permissible Signal Source Impedance
This LSI's analog input is designed such 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 A/D conversion precision. However, for A/D conversion in single mode with
a large capacitance provided externally for A/D conversion in single mode, the input load will
essentially comprise only the internal input resistance of 3 kΩ, and the signal source impedance is
ignored. However, as 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) (see
figure 21.10). When converting a high-speed analog signal, a low-impedance buffer should be
inserted.
Rev. 1.00 Mar. 25, 2008 Page 1057 of 1868
REJ09B0372-0100