LX2208ILD データシートの表示（PDF） - Microsemi Corporation

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LX2208ILD

2 Amp Three Level Lithium Ion Battery Charger

Microsemi Corporation 

LX2208

2 Amp Three Level Lithium Ion Battery Charger

®

TM

PRODUCTION DATA SHEET

APPLICATION NOTE

BATTERY TEMPERATURE MONITOR

The LX2208 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 within a temperature

range of 0°C to 60°C. For this calculation, a Vishay

NTHS0402N01N1003J Thermistor was used. This

thermistor has the value of 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 TMP thresholds. A

fixed value resistor is added in series with the

thermistor to prevent it from becoming too low

impedance at high temperatures and causing the TMP

input to default to off.

VTH

RTH

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 = 122k

K

TMP

RMIN

R2 = R1 × R TH = 14,800k

R1 − R TH

RNTC

In this case, it is not necessary to use R2, because the

value is so large it is insignificant. In this case, R1 = RTH.

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, using Cold

Temperature Fault Threshold average of 74% and the

Hot Temperature Fault Threshold average of 29% of

VIN:

( ) VTH = 0.29 × 0.74 × R T=0°C − R T=60°C

( ) ( ) VIN 0.29 × R T=0°C − 0.74 × R T=60°C

= K = 0.99

R TH

=

⎜⎛ K

⎝ 0.74

−

1⎟⎞

⎠

×

R

T=0ºC

= 121k

The final circuit for this example is:

TMP

VIN

121k

24.9k

RNTC

The TMP voltages with this circuit are:

TEMP (°C)

RNTC

VTMP (%VIN)

-20

971k

89%

0

327k

74%

25

100k

51%

60

24.9k

29%

80

12.6k

24%

Where R at temperature is the sum of the thermistor

plus RMIN.

At the trip point threshold, there may be chattering on

and off of the charging current. However, as the

temperature increases or decreases further from the trip

point threshold, the chattering will stop.

Copyright © 2007

Rev. 1.0, 2007-04-03

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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