LTC4100EGPBF LINER [Linear Technology], LTC4100EGPBF Datasheet - Page 21

• Manufacturer Part Number: LTC4100EGPBF
• Description: Smart Battery Charger Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Adapter Limiting
An important feature of the LTC4100 is the ability to auto-
matically adjust charging current to a level which avoids
overloading the wall adapter. This allows the product to
operate at the same time that batteries are being charged
without complex load management algorithms. Addition-
ally, batteries will automatically be charged at the maximum
possible rate of which the adapter is capable.
This feature is created by sensing total adapter output
current and adjusting charging current downward if a
preset adapter current limit is exceeded. True analog
control is used, with closed loop feedback ensuring that
adapter load current remains within limits. Amplifi er CL1 in
Figure 9 senses the voltage across R
tween the CLP and CLN pins. When this voltage exceeds
100mV, the amplifi er will override programmed charging
current to limit adapter current to 100mV/R
fi lter formed by 4.99k and 0.1μF is required to eliminate
switching noise. If the current limit is not used, CLP should
be connected to CLN.
Setting Input Current Limit
To set the input current limit, you need to know the mini-
mum wall adapter current rating. Subtract 7% for the input
current limit tolerance and use that current to determine
the resistor value.
Table 8. Common RCL Resistor Values
* Rounded to nearest 5% standard step value. Many non standard values are popular.
ADAPTER RATING (A) –7% ADAPTER RATING (A)
R
I
LIM
CL
= 100mV/I
= Adapter Min Current
1.5
1.8
2.0
2.3
2.5
2.7
3.0
3.3
3.6
4.0
– (Adapter Min Current • 7%)
LIM
1.40
1.67
1.86
2.14
2.33
2.51
2.79
3.07
3.35
3.72
CL
, connected be-
R
CL
CL
VALUE* (Ω) 1%
. A lowpass
0.068
0.062
0.051
0.047
0.043
0.039
0.036
0.033
0.030
0.027
R
As is often the case, the wall adapter will usually have at
least a +10% current limit margin and many times one
can simply set the adapter current limit value to the actual
adapter rating (Figure 9).
Charge Termination Issues
Batteries with constant current charging and voltage-based
charger termination might experience problems with re-
ductions of charger current caused by adapter limiting. It
is recommended that input limiting feature be defeated in
such cases. Consult the battery manufacturer for informa-
tion on how your battery terminates charging.
Setting Output Current Limit (Refer to Figure 1)
The LTC4100 current DAC and the PWM analog circuitry
must coordinate the setting of the charger current. Failure
to do so will result in incorrect charge currents.
CL
LIMIT (A) R
1.47
1.61
1.96
2.13
2.33
2.56
2.79
3.07
3.35
3.72
*R
LTC4100
CL
=
ADAPTER CURRENT LIMIT
CL1
CL
Figure 9. Adaptor Current Limiting
POWER DISSIPATION (W) R
100mV
–
+
+
100mV
0.15
0.16
0.20
0.21
0.23
0.26
0.28
0.31
0.33
0.37
24
23
4
CLP
CLN
INFET
4.99k
C9
0.1μF
R1
TO LOAD
CL
LTC4100
R
POWER RATING (W)
CL
4100 F09
*
0.25
0.25
0.25
0.25
0.50
0.50
0.50
0.50
0.50
0.50
21
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IN
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