LTC4101 Datasheet, PDF (22/28 Pages) Linear Technology – Smart Battery Charger Controller

LTC4101
APPLICATIO S I FOR ATIO
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.
Warning
DO NOT CHANGE THE VALUE OF R_ILIM DURING OPERA-
TION. The value must remain fixed and track the R_SENSE
value at all times. Changing the current setting can result
in currents that greatly exceed the requested value and
potentially damage the battery or overload the wall adapter
if no input current limiting is provided.
Setting Output Current Limit (Refer to Figure 1)
The LTC4101 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 9. Recommended Resistor Values
I_MAX (A)
1.023
R_SENSE (Ω) 1% R_SENSE (W)
0.100
0.25
2.046
0.05
0.25
3.068
0.025
0.5
4.092
0.025
0.5
R_ILIM (Ω) 1%
0
10k
33k
Open
Inductor Selection
Higher operating frequencies allow the use of smaller
inductor and capacitor values. A higher frequency gener-
ally results in lower efficiency because of MOSFET gate
charge losses. In addition, the effect of inductor value on
ripple current and low current operation must also be
considered. The inductor ripple current ∆I_L decreases
with higher frequency and increases with higher V_IN.
∆I_L
=
1
(^f)(^L)
V_OUT
⎛⎝⎜_1−
V_OUT
V_IN
⎞
⎠⎟
Table 8. Common R_CL Resistor Values
Adapter
Rating (A)
–7% Adapter
Rating (A)
R_CL Value*
(Ω)1%
R_CL
Limit (A)
1.5
1.40
0.068
1.47
1.8
1.67
0.062
1.61
2.0
1.86
0.051
1.96
2.3
2.14
0.047
2.13
2.5
2.33
0.043
2.33
2.7
2.51
0.039
2.56
3.0
2.79
0.036
2.79
3.3
3.07
0.033
3.07
3.6
3.35
0.030
3.35
4.0
3.72
0.027
3.72
* Rounded to nearest 5% standard step value. Many non standard values are popular.
R_CLPower
Dissipation (W)
0.15
0.16
0.20
0.21
0.23
0.26
0.28
0.31
0.33
0.37
R_CL Power
Rating(W)
0.25
0.25
0.25
0.25
0.50
0.50
0.50
0.50
0.50
0.50
4101f
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