Datasheet

LTC4098-3.6
24
409836f
By using a bias resistor, R
NOM
, different in value from
R25, the hot and cold trip points can be moved in either
direction. The temperature span will change somewhat due
to the nonlinear behavior of the thermistor. The following
equations can be used to easily calculate a new value for
the bias resistor:
RR
RR
NOM
HOT
NOM
COLD
=
=
α
α
025
25
326
25
.
•
.
•
where a
HOT
and a
COLD
are the resistance ratios at the
desired hot and cold trip points. Note that these equations
Solving these equations for R
NTC|COLD
and R
NTC|HOT
results in the following:
R
NTC|HOT
= 0.25 • R
NOM
and
R
NTC|COLD
= 3.26 • R
NOM
By setting R
NOM
equal to R25, the previous equations
result in
a
HOT
= 0.25 and a
COLD
= 3.26. Referencing
these ratios to the Vishay Resistance-Temperature curve
1 chart gives a hot trip point of about 60°C and a cold trip
point of about 0°C. The difference between the hot and
cold trip points is approximately 60°C.
–
+
–
+
R
NOM
100k
R
NTC
100k
NTC
0.1V
NTC_ENABLE
409836 F09a
LTC4098-3.6 NTC BLOCK
TOO_COLD
TOO_HOT
0.765 • NTCBIAS
0.199 • NTCBIAS
–
+
5
NTCBIAS
4
T
–
+
–
+
R
NOM
102k
R
NTC
100k
R1
8.06k
NTC
0.1V
NTC_ENABLE
409836 F09b
TOO_COLD
TOO_HOT
0.765 • NTCBIAS
0.199 • NTCBIAS
–
+
5
T
NTCBIAS
4
LTC4098-3.6 NTC BLOCK
(9a) (9b)
Figure 9. NTC Circuits
APPLICATIONS INFORMATION