lx2208 Microsemi Corporation, lx2208 Datasheet - Page 9

• Manufacturer Part Number: lx2208
• Description: 2 Amp Three Level Lithium Ion Battery Charger
• Manufacturer: Microsemi Corporation

Copyright © 2007
Rev. 1.0, 2007-04-03
B
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.
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.
temperature at 60°C works well; therefore, for this
example, set the value of R
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 R
Temperature Fault Threshold average of 74% and the
Hot Temperature Fault Threshold average of 29% of
V
plus R
ATTERY
IN
The LX2208 has an input to monitor the battery
Using a value of R
:
Where R at temperature is the sum of the thermistor
MIN
=
V
V
TM
.
TH
IN
K
T
EMPERATURE
=
=
R
0.99
(
TH
0.29
0.29
=
TMP
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
⎛
⎜
⎝
×
×
MIN
0.74
0.74
R
K
TH
T
=
that is equal to the thermistor
0
−
M
and V
°
×
C
1
V
MIN
ONITOR
(
) (
⎞
⎟
⎠
R
TH
−
×
T
R
R
R
R
to 24.9k. This has the
0.74
=
MIN
TH
NTC
0
T
TH
°
=
C
0º
C
−
×
are, using Cold
=
R
R
121k
T
T
=
60
=
60
A P P L I C A T I O N N O T E
°
C
°
C
Analog Mixed Signal Group
)
)
Microsemi
This
®
2 Amp Three Level Lithium Ion Battery Charger
value is so large it is insignificant. In this case, R1 = R
The TMP voltages with this circuit are:
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.
Thevenin Voltage and resistance using a voltage
divider from the input pin (IN).
The values of R1 and R2 can be calculated as:
In this case, it is not necessary to use R2, because the
The final circuit for this example is:
TEMP (°C)
To finish the design it is necessary to create the
-20
25
60
80
0
P
RODUCTION
TMP
R2
R1
=
TMP
24.9k
12.6k
971k
327k
100k
R
R
R
=
1
NTC
1
V
×
−
R
K
IN
R
R
TH
R
D
R1
R
TH
TH
V
NTC
MIN
ATA
=
IN
=
24.9k
121k
122k
R
14,800k
NTC
V
S
TMP
HEET
89%
74%
51%
29%
24%
R2
(%
V
IN
)
LX2208
TH
.
Page 9