LTC4101EG View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4101EG' PDF : 30 Pages View PDF
LTC4101
APPLICATIONS INFORMATION
Table 8. Recommended Resistor Values
Adapter
Rating (A)
–7% Adapter
Rating (A)
RCL Value*
(Ω)1%
RCL
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.
RCLPower
Dissipation (W)
0.15
0.16
0.20
0.21
0.23
0.26
0.28
0.31
0.33
0.37
RCL Power
Rating(W)
0.25
0.25
0.25
0.25
0.50
0.50
0.50
0.50
0.50
0.50
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 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
IMAX (A)
RSENSE (Ω) 1%
RSENSE (W)
1.023
0.100
0.25
2.046
0.05
0.25
3.068
0.025
0.5
4.092
0.025
0.5
RILIM (Ω) 1%
0
10k
33k
Open
Warning
DO NOT CHANGE THE VALUE OF RILIM DURING OPERA-
TION. The value must remain fixed and track the RSENSE
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.
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 ΔIL decreases with
higher frequency and increases with higher VIN.
ΔIL
=
1
(f)(L)
VOUT
⎛
⎝⎜
1−
VOUT
VIN
⎞
⎠⎟
Accepting larger values of ΔIL allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is ΔIL = 0.4(IMAX). Remember the
maximum ΔIL occurs at the maximum input voltage. The
inductor value also has an effect on low current operation.
The transition to low current operation begins when the
inductor current reaches zero while the bottom MOSFET
is on. Lower inductor values (higher ΔIL) will cause this
to occur at higher load currents, which can cause a dip in
efficiency in the upper range of low current operation.
4101fa
22
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