LX2205 データシートの表示（PDF） - Microsemi Corporation

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LX2205

1A Li-Ion Battery Charger with Power Source Management

Microsemi Corporation 

LX2205

® 1A Li-Ion Battery Charger with Power Source Management

TM

PRODUCTION DATA SHEET

APPLICATION NOTE

BATTERY TEMPERATURE MONITOR

The LX2205 has an input to monitor the battery

temperature during battery charging. The SYS voltage

must be used to bias this circuitry. During the occurrence of

a TMP fault, the charge cycle is suspended; however the

status indicators state remains unchanged.

A typical Lithium Ion battery should only be charged

within a temperature range of 0°C to 60°C. For this

calculation example, 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.

To finish the design it is necessary to create the Thevenin

Voltage and resistance using a voltage divider from the

SYS pin.

The values of R1 and R2 can be calculated as:

R1 =

RTH

K

= 88k

R2

= R1 × RTH

R1 − RTH

= 958k

Actual standard 1% resistor values are: 953k and

88.7k. The final circuit for this example is:

VSYS

TMP

88.7k

12.4k

RNTC

953k

Using a value of RMIN that is ½ the thermistor high

temperature trip resistance value works well; therefore, for

this example, set the value of RMIN to:

12.4k = RMIN

=

RT =60°C

2

.

This has the effect of adding a fixed 12.4k to the

thermistor resistance values so it becomes 339kΩ at 0°C,

112kΩ at 25°C and 37.3kΩ 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 VSYS:

( ) VTH

=

0.29 × 0.74 ×

R − R T =0°C

T =60°C

( ) ( ) VSYS 0.29 × RT =0°C − 0.74 × RT =60°C

= K = 0.916

The TMP voltages with this circuit are:

TEMP (°C)

-20

0

25

60

80

RNTC

971k

327k

100k

24.9k

12.6k

VTMP (% VSYS)

85%

74%

53%

29%

22%

RTH

=

⎜⎛

⎝

K

0.74

−1⎟⎞

⎠

×

RT

= 0° C

= 80.6k

Copyright © 2007

Rev. 1.0a, 2007-03-02

Microsemi

Analog Mixed Signal Group

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 12

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