Renesas M32R/ECU Series, User Manual

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11
11-45
A-D Converters
32180 Group User's Manual (Rev.1.0)
11.5 Precautions on Using A-D Converters
Table 11.5.1 Sampling Time (in Which C2 Needs to Be Charged)
Conversion start method Conversion speed Sampling time for the first bit Sampling time for the second and subsequent bits
Single mode Slow mode Normal speed 27.5BCLK 13.5BCLK
(when sample-and Double speed 15.5BCLK 7.5BCLK
-hold disabled) Fast mode Normal speed 11.5BCLK 5.5BCLK
Double speed 7.5BCLK 3.5BCLK
Single mode Slow mode Normal speed 27.5BCLK –
(when sample-and Double speed 15.5BCLK –
-hold enabled) Fast mode Normal speed 11.5BCLK –
Double speed 7.5BCLK –
Comparator mode Slow mode Normal speed 27.5BCLK –
Double speed 15.5BCLK –
Fast mode Normal speed 11.5BCLK –
Double speed 7.5BCLK –
Therefore, the time in which C2 needs to be charged is found from Eq. B-1, as follows:
Sampling time (in which C2 needs to be charged) > Cin
×
R1 + C2(R1 + R2) --- Eq. B2
Thus, the maximum value of R1 can be obtained as a criterion from the equation below. Note, however, that
for single mode (when sample-and-hold is disabled), the sampling time for the second and subsequent bits
(C2 charging time) must be applied.
C2 charging time - C2
×
R2
R1 <
Cin + C2