LTC4069EDC-4.4-PBF LINER [Linear Technology], LTC4069EDC-4.4-PBF Datasheet - Page 14

• Manufacturer Part Number: LTC4069EDC-4.4-PBF
• Manufacturer: LINER [Linear Technology]

LTC4069-4.4
APPLICATIONS INFORMATION
Thermistors
The LTC4069-4.4 NTC trip points are designed to
work with thermistors whose resistance-temperature
characteristics follow Vishay Dale’s “R-T Curve 1.” The
Vishay NTHS0603N01N1003J is an example of such a
thermistor. However, Vishay Dale has many thermistor
products that follow the “R-T Curve 1” characteristic in a
variety of sizes. Furthermore, any thermistor whose ratio
of R
Curve 1 shows a ratio of R
= 6.13).
Designers may want to use thermistors whose room
temperature value is different than 100k. Vishay Dale has
a number of values of thermistor from 32k to 100k that
follow the “R-T Curve 1.” Using different R-T curves, such
as Vishay Dale “R-T Curve 2”, is also possible. This curve,
combined with LTC4069-4.4 internal thresholds, gives
temperature trip points of approximately –3°C (falling) and
42°C (rising), a delta of 45°C. This delta in temperature
can be moved in either direction by changing the value of
R
both trip points to higher temperatures.
14
NOM
COLD
with respect to R
R
8.87k
R1
604Ω
NOM
R
10k
to R
NTC
6
0.016 • V
HOT
0.76 • V
0.35 • V
NTC
is about 6 will also work (Vishay Dale R-T
CC
CC
CC
Figure 6. NTC Circuits
V
CC
NTC
COLD
. Increasing R
–
+
–
+
+
–
to R
HOT
of 3.266/0.5325
NOM
TOO HOT
NTC_ENABLE
TOO COLD
will move
4069 F06
To calculate R
example, use the following equation:
where R
cold temperature trip point. If you want to shift the trip points
to higher temperatures use the following equation:
where R
hot temperature trip point.
Here is an example using a 10k R-T Curve 2 thermistor
from Vishay Dale. The difference between the trip points
is 45°C, from before, and we want the cold trip point to
be 0°C, which would put the hot trip point at 45°C. The
R
The nearest 1% value for R
used to bias the NTC thermistor to get cold and hot trip
points of approximately 0°C and 45°C respectively. To
extend the delta between the cold and hot trip points, a
resistor, R1, can be added in series with R
6). The values of the resistors are calculated as follows:
where R
R
trip points. Continuing the example from before with a
desired trip point of 50°C:
NOM
COLD
R
R
R
R
R
NOM
NOM
NOM
NOM
1
needed is calculated as follows:
=
are the values of R
COLD
NOM
HOT
⎛
⎝ ⎜
=
=
=
=
=
3 266
R
R
3 266
0 5325
3 266
3 266 0 5325
.
2 816
3
is the resistance ratio of R
is the value of the bias resistor and R
R
R
COLD
is the resistance ratio of R
.
COLD
.
.
.
.
. .
COLD
HOT
266
NOM
0 5325
.
− −
−
0 5325
for a shift to lower temperature for
•
•
•
−
•
.
R
R
10
R
.
R
NTC
NTC
HOT
NTC
k
NTC
=
NOM
at
at
⎞
⎠ ⎟
8 62
at
.
at the desired temperature
• R
25
25
25
is 8.66k. This is the value
(
°
°
k
COLD
C
C
°
C
NTC
NTC
−
NTC
R
at the desired
at the desired
HOT
(see Figure
)
−
HOT
R
406944fa
HOT
and