LAPIS Semiconductor ML610472, Руководство пользователя

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ML610471/472/473/Q471/Q472/Q473 User's Manual
Chapter 17 RC Oscillation Type A/D Converter
17-14
The ratio between f
RCCLK
(RT1) and f
RCCLK
(RS1) is equivalent to the above-mentioned A/D conversion value nT0 that
should ideally depend only on RT1.
Ref
er
enc
e r
es
is
ta
n
ce
R
S
1
Temperature T
f
RCC LK
(RT1)
Temperature T
Ideal
Includes errors due to factors other
than RT1
f
RCLK
(RS1) =
k
R CCLK
·(CS1+CVR)·RT1
1
Figure 17-8 Temperature Characteristics of
Reference Resistor
Figure 17-9 Oscillation Characteristics of
Thermistor
Temperature T
Includes errors due to factors
other than RT1
f
RCC LK
(RS1) =
k
R CCLK
·(CS1+CVR)·RS1
1
Ideal
f
RCLK
(RS1)
Figure 17-10 Oscillation Characteristics of Reference Resistor
Figure 17-11 shows, as an example of method, a timing chart of one cycle of conversion from analog value RT1 to a
digital value, that is, A/D conversion.
Basically, one A/D conversion cycle must consist of two steps, as shown in Figure 17-11. The reason for requiring two
steps is that the reference resistor and the thermistor must first be oscillated separately and then the ratio between the
oscillation frequencies of them is used, as described above.
In the example below, operation for these two steps is performed using the following combination:
•First step = RC oscillation with RS1 in Counter A reference mode
•Second step = RC oscillation with RT1 in Counter B reference mode
Besides this, there would be several possible A/D conversion methods.
In the above method, the operation time (gate time) for the second step fluctuates depending on the value of thermistor
RT1. To avoid the fluctuation of the operation time, using a method that uses the following combination is
recommended:
•First step = RC oscillation with RS1 in Counter B reference mode
•Second step = RC oscillation with RT1 in Counter A reference mode
A/D conversion procedure is explained below by taking Figure 17-11 as an example.