Datasheet

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last update
November 30, 2010
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7.2 Mode 6. Ther: 1 thermistor, 4-wire
In this mode, one thermistor and one reference resistor can be measured. The connection of the
thermistor and the reference resistor is shown in Figure 10 .
The driving voltage V
EF
is a chopped voltage with an amplitude of V
DD
/12.5 (0.4 V at V
DD
= 5 V)
and a DC value V
DD
/2.
The ratio of the thermistor and the reference resistor is also given by (3). The signals, which are
measured during the various phases, are listed in Table 12 . The voltage V
AB
is not constant, but has the
same temperature information as V
CD
, which linearises the sensor characteristic.

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

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

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 
  a) b) c)
Figure 10. Connection of the thermistor to the UTI in a 4-wire (a), 3-wire (b) and 2-wire (c)
connection
Parameter (V
DD
= 5 V) Typical value
K
2
56 s/V
V
0
0.36 V
R
ref
//R
x
<5 k
R
ref
+R
x
>1 k
Offset 10 V
Linearity 13 bits
Resolution (SF = 0) 7 mV (1 mK)
Table 14. Specifications of the Ther mode
The specification of the thermistor mode is shown in Table 14. For very large and very small values of
R
x
(10 times or 0.1 times Rref ), the resolution, in voltage, is still the same, but the resolution in
temperature is decreased. This is due to the linearization method.
For a thermistor with a sensitivity of 4%/K, the resolution is 1 mK for V
DD
= 5 V.
E
A
B
C
D
F
 
R
REF
R
X
E
A
B
C
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
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 
R
REF
R
X
E
A
B
C
D
F
 

R
REF
R
X