ltc4069edc-4.4 Linear Technology Corporation, ltc4069edc-4.4 Datasheet - Page 14

• Manufacturer Part Number: ltc4069edc-4.4
• Description: Standalone 750ma Li-ion Battery Charger In 2 ? 2 Dfn With Ntc Thermistor Input
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC4069-4.4
Thermistors
The LTC4069-4.4 NTC trip points are designed to work
with thermistors whose resistance-temperature charac-
teristics follow Vishay Dale’s “R-T Curve 1.” The Vishay
NTHS0603NO1N1002J is an example of such a ther-
mistor. However, Vishay Dale has many thermistor prod-
ucts 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).
Power conscious designs may want to use thermistors
whose room temperature value is greater than 10k. Vishay
Dale has a number of values of thermistor from 10k to
100k that follow the “R-T Curve 1.” Using different R-T
curves, such as Vishay Dale “R-T Curve 2”, is also pos-
sible. This curve, combined with LTC4069-4.4 internal
thresholds, gives temperature trip points of approximately
0°C (falling) and 40°C (rising), a delta of 40°C. This delta
in temperature can be moved in either direction by chang-
ing the value of R
R
14
COLD
NOM
will move both trip points to higher temperatures.
to R
R
8.87k
R1
604Ω
NOM
R
10k
NTC
HOT
6
0.016 • V
0.76 • V
0.35 • V
NTC
is about 5 will also work (Vishay Dale R-T
CC
CC
CC
NOM
Figure 6. NTC Circuits
U
V
CC
with respect to R
U
COLD
–
+
–
+
+
–
to R
W
HOT
of 3.266/0.5325 =
NTC
TOO HOT
NTC_ENABLE
TOO COLD
. Increasing
U
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 100k R-T Curve 2 thermistor
from Vishay Dale. The difference between the trip points is
40°C, from before, and we want the cold trip point to be
0°C, which would put the hot trip point at 40°C. The R
needed is calculated as follows:
The nearest 1% value for R
used to bias the NTC thermistor to get cold and hot trip
points of approximately 0°C and 40°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:
COLD
R
R
R
R
R
NOM
NOM
NOM
NOM
1
=
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
406944f
HOT
NOM
and