LTC4001-1 Linear Technology, LTC4001-1 Datasheet - Page 12

• Manufacturer Part Number: LTC4001-1
• Description: 2A Synchronous Buck Li-Ion Charger
• Manufacturer: Linear Technology

www.DataSheet4U.com
APPLICATIONS INFORMATION
LTC4001-1
The battery temperature is measured by placing a negative
temperature coeffi cient (NTC) thermistor close to the bat-
tery pack. To use this feature, connect the NTC thermistor,
R
R
resistor with a value equal to the value of the chosen NTC
thermistor at 25°C. The LTC4001-1 goes into hold mode
when the resistance, R
0.41 times the value of R
(The value for a Vishay NTHS0603N02N1002J thermistor
at 25°C) hold occurs at approximately 4.1k, which occurs
at 50°C. The hold mode freezes the timer and stops the
charge cycle until the thermistor indicates a return to a
valid temperature. As the temperature drops, the resistance
of the NTC thermistor rises. The LTC4001-1 is designed to
go into hold mode when the value of the NTC thermistor
increases to 2.82 times the value of R
is R
which corresponds to approximately 0°C. The hot and cold
comparators each have approximately 3°C of hysteresis
to prevent oscillation about the trip point. Grounding the
NTC pin disables the NTC function.
Thermistors
The LTC4001-1 NTC trip points were designed to work with
thermistors whose resistance temperature characteristics
follow Vishay Dale’s “R-T Curve 2.” However, any thermis-
tor whose ratio of R
(Vishay Dale R-T Curve 2 shows a ratio of R
of 2.815/0.4086 = 6.89).
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 these as indicated
in the NTC Thermistor section will give temperature trip
points of approximately 3°C and 47°C, a delta of 44°C. This
delta in temperature can be moved in either direction by
changing the value of R
12
NTC
NOM
COLD
, between the NTC pin and GNDSENS and the resistor,
, from the NTC pin to V
. For the Vishay 10k thermistor, this value is 28.2k,
COLD
NOM
HOT
NOM
to R
, of the NTC thermistor drops to
with respect to R
INSENSE
. For instance for R
HOT
is about 7 will also work
. R
NOM
NOM
. This resistance
should be a 1%
NTC
COLD
. Increasing
NTC
to R
= 10k.
HOT
R
calculate R
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 1 thermistor
from Vishay Dale. The difference between trip points is
44°C, from before, and we want the cold trip point to be
0°C, which would put the hot trip point at 44°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 44°C respectively. To
extend the delta between the cold and hot trip points a
resistor, R1, can be added in series with R
The values of the resistors are calculated as follows:
NOM
R
R
R
R
R1=
NOM
NOM
NOM
NOM
will move the trip points to higher temperatures. To
2.815 – 0.4086
COLD
HOT
=
=
=
=
=
NOM
R
0.4086
R
2.815 – 0.4086
2.815
2.815
3.266
2.815
R
0.4086
R
is the resistance ratio of R
COLD
COLD
is the resistance ratio of R
COLD
HOT
for a shift to lower temperature for example,
• 100k = 116k
• R
• R
– R
• R
NTC
NTC
NTC
HOT
• R
(
at 25°C
at 25°C
at 25°C
NOM
COLD
is 115k. This is the value
– R
HOT
NTC
NTC
NTC
)
– R
(see Figure 4).
at the desired
at the desired
HOT
40011fa
NOM