sider a 10kΩ (at +25°C) NTC thermistor in series with a
5110Ω resistor operating at +40°C with a constant 5V
bias. If it is one of the standard thermistors in Table 2,
its resistance is 5325Ω at this temperature. The power
dissipated in the thermistor is:
(5)
2
(5325) / (5325 + 5110)
2
= 1.22mW
This thermistor would therefore have a self-heating
error at +40°C of 1.22°C. Because the MAX6682 uses a
small reference voltage and energizes the thermistor
less than 2% of the time, the self-heating of the thermis-
tor under the same conditions when used with the
MAX6682 is only:
(1.22)
2
(5325)(0.02) / (5325 + 5110)
2
=1.46µW, or only about 0.0015° (self-heating
error)
MAX6682
Thermistor-to-Digital Converter
_______________________________________________________________________________________ 7
CS
SCK
1
SO
B10
MSB
B9 B1B2B8 B7 B6 B4B5 B3
B0
LSB
t
TR
t
DO
t
DV
t
CSS
t
CH
t
CL
Figure 5. Serial Interface Timing
Table 3. Temperature vs. Digital Output for Standard Thermistor with R
EXT
= 5110Ω
MANUFACTURER PART WEBSITE
Betatherm 10K3A1 www.betatherm.com
Dale 1M1002
www.vishay.com/brands/
dale/main.html
Thermometrics C100Y103J www.thermometrics.com
Table 2. Standard Thermistors
THERMISTOR
TEMPERATURE
(°C)
V
REXT
(mV) WITH
STANDARD THERMISTOR
AND R
EXT
= 5110Ω*
DECIMAL VALUE OF D
OUT
(USING 1LSB = 0.125°C)
D
OUT
+75.000 946.0 57.75 001 1100 1110
+70.000 908.6 54.875 001 1011 0111
+60.000 820.6 47.875 001 0111 1111
+50.000 715.7 39.625 001 0011 1101
+40.000 597.4 30.25 000 1111 0010
+30.000 473.5 20.5 000 1010 0100
+25.000 412.6 15.750 000 0111 1110
+20.000 354.1 11.125 000 0101 1001
+10.000 249.2 2.875 000 0001 0111
0 165.1 -3.750 111 1110 0010
-5.000 131.5 -6.375 111 1100 1101
