
11
A/D CONVERTER
11-49
32185/32186 Group Hardware Manual
Rev.1.10 REJ09B0235-0110 May 15, 07
11.5 Notes on Using A/D Converter
Table 11.5.1 Sampling Time (in Which C2 Needs to Be Charged)
Conversion start method
Conversion speed
Sampling time
Sampling time for the
for the first bit
2nd and subsequent bits
2BCLK mode
Single mode
Slow mode
Normal speed
55BCLK
27BCLK
(when sample-and-hold
Double speed
31BCLK
15BCLK
disabled or normal
Fast mode
Normal speed
23BCLK
11BCLK
sample-and-hod enabled
Double speed
15BCLK
7BCLK
Single mode
Slow mode
Normal speed
55BCLK
–
(when fast sample-
Double speed
31BCLK
–
and-hold enabled)
Fast mode
Normal speed
23BCLK
–
Double speed
15BCLK
–
Comparator mode
Slow mode
Normal speed
55BCLK
–
Double speed
31BCLK
–
Fast mode
Normal speed
23BCLK
–
Double speed
15BCLK
–
Simultaneous
Slow mode
Normal speed
55BCLK
–
sampling
Double speed
31BCLK
–
Fast mode
Normal speed
23BCLK
–
Double speed
15BCLK
–
BCLK mode
Single mode
Slow mode
Normal speed
27.5BCLK
13.5BCLK
(when sample-and-hold
Double speed
15.5BCLK
7.5BCLK
disabled or normal
Fast mode
Normal speed
11.5BCLK
5.5BCLK
sample-and-hod enabled
Double speed
7.5BCLK
3.5BCLK
Single mode
Slow mode
Normal speed
27.5BCLK
–
(when fast sample-
Double speed
15.5BCLK
–
and-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
–
Simultaneous
Slow mode
Normal speed
27.5BCLK
–
sampling
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. B-2
Thus, the maximum value of R1 can be obtained as a criterion from the equation below. Note, how-
ever, 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