Rohm LAPIS SEMICONDUCTOR ML620Q503, User Manual

Page: 456 / 553

ML620Q503/Q504 User's Manual
Chapter 24 RC Oscillation Type A/D Converter
FEUL620Q504 24-17
24.3.3 Example of Use of RC Oscillation Type A/D Converter
This section describes the method of performing A/D conversion for sensor values in Counter A and B reference
modes by taking temperature measurement by a thermistor as an example.
Figure 24-8 shows the configuration of 1-thermistor RC oscillator circuit using RCOSC0.
Figure 24-8 Configuration of 1-Thermistor RC Oscillator Circuit Using RCOSC0
Figure 24-9 shows the temperature characteristics of the thermistor resistance RT0.
RT
0
T
her
m
is
tor
R
es
is
tan
c
e
Temperature T
RT0=f(T)
n
T
0
D
ig
it
a
l v
a
lu
e
RT0
nT0=K
･
RT0
=K
･
f(T)
Figure 24-9 Temperature Characteristics of
Thermistor
Figure 24-10 A/D Conversion Characteristics
(Ideal characteristics when nT0 is
proportional to RT0)
RT0 is expressed as a function of temperature T by the following equation:
RT0 = f (T)
Figure 24-10 shows the ideal characteristics of A/D conversion with the assumption that RT0 is an analog
quantity. In the ideal characteristics, the A/D conversion value nT0 will purely depend on RT0 only. Assuming
that nT0 is proportional to RT0, let proportional constant be K, then nT0 has the following relationship with
temperature T:
nT0 = K•RT0 = K•f (T) ... Expression A
Therefore, temperature T can be expressed as a digital value by performing the conversion processing that accord
with the characteristics shown in Figure 24-9 for nT0 by software.
CS0
RS0
RT0
IN0
CS0
Reference resistor RS0
Thermistor RT0