LLTC4100EG View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LLTC4100EG' PDF : 30 Pages View PDF
LTC4100
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. Amplifier CL1 in
Figure 9 senses the voltage across RCL, connected be-
tween the CLP and CLN pins. When this voltage exceeds
100mV, the amplifier will override programmed charging
current to limit adapter current to 100mV/RCL. A lowpass
filter 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.
RCL = 100mV/ILIM
ILIM = Adapter Min Current
– (Adapter Min Current • 7%)
LTC4100
CLP
24
VIN
CL1
CLN
C9
0.1µF
RCL*
23
100mV
R1
4.99k
INFET
4
TO LOAD
*RCL
=
ADAPTER
100mV
CURRENT
LIMIT
4100 F09
Figure 9. Adaptor Current Limiting
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 reductions of charger current caused by adapter
limiting. It is recommended that input limiting feature be
defeated in such cases. Consult the battery manufacturer
for information 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.
Table 8. Common RCL Resistor Values
ADAPTER RATING (A) –7% ADAPTER RATING (A) RCL VALUE* (Ω) 1% RCL LIMIT (A) RCL POWER DISSIPATION (W) RCL POWER RATING (W)
1.5
1.40
0.068
1.47
0.15
0.25
1.8
1.67
0.062
1.61
0.16
0.25
2.0
1.86
0.051
1.96
0.20
0.25
2.3
2.14
0.047
2.13
0.21
0.25
2.5
2.33
0.043
2.33
0.23
0.50
2.7
2.51
0.039
2.56
0.26
0.50
3.0
2.79
0.036
2.79
0.28
0.50
3.3
3.07
0.033
3.07
0.31
0.50
3.6
3.35
0.030
3.35
0.33
0.50
4.0
3.72
0.027
3.72
0.37
0.50
* Rounded to nearest 5% standard step value. Many nonstandard values are popular.
4100fc
For more information www.linear.com/LTC4100
21
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