LX2207ILD データシートの表示（PDF） - Microsemi Corporation
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LX2207ILD Datasheet PDF : 14 Pages
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LX2207
Three Level Lithium Ion Battery Charger
®
TM
PRODUCTION DATA SHEET
APPLICATION NOTE
BATTERY TEMPERATURE MONITOR
The LX2207 has an input to monitor the battery
temperature during battery charging; this method
assumes the battery pack contains a thermistor
expressly for this purpose. A typical Lithium ion battery
should only be charged from a range of 0°C to 60°C.
For this calculation, a Vishay NTHS0402N01N1003J
Thermistor was used. This thermistor is 327kΩ at 0°C,
100kΩ at 25°C and 24.9kΩ at 60°C. The thermistor
must be biased with a Thevenin voltage source and
series resistance to achieve the proper thresholds. A
fixed value resistor is added in series with the
thermistor to prevent it from becoming too low an
impedance at high temperatures and causing the TMP
input to default to off.
VTH
TMP
RTH
RMIN
RNTC
Using a value of RMIN that is equal to the thermistor
temperature at 60°C works well; therefore, for this
example, set the value of RMIN to 24.9k. This has the
effect of adding 24.9k to the thermistor resistance
values so it becomes 352kΩ at 0°C, 125kΩ at 25°C and
49.8kΩ at 60°C.
The equations for RTH and VTH are:
VTH
VIN
=
0.29 × 0.74 × (RT=0C − RT=60C )
(0.29 ×RT=0C )− (0.74 ×RT=60C )
= K = 0.99
RTH
=
⎜⎛
⎝
K
0.74
− 1⎟⎞
⎠
× RT=0C
=
121k
Where R at temperature is the sum of the thermistor
plus RMIN.
To finish the design it is necessary to create the
Thevenin Voltage and resistance using a voltage
divider from the input pin (IN).
VIN
R1
TMP
RMIN
R2
RNTC
The values of R1 and R2 can be calculated as:
R1
=
RTH
K
= 122k
R2
=
R1 × RTH
R1 − RTH
= 14,800k
In this case, it is not necessary to use R2, because the
value is so large it is insignificant. In this case, R1 = RTH.
The final circuit for this example is:
VIN
TMP
121k
24.9k
RNTC
The TMP voltages with this circuit are:
TEMP (°C)
-20
0
25
60
80
RNTC
971k
327k
100k
24.9k
12.6k
VTMP (%VIN)
89%
74%
51%
29%
24%
Copyright © 2007
Rev. 1.0a, 2007-10-08
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
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