SLUSA27 – MARCH 2010
Table 11. Charge Current Settings for 68-mΩ and 100-mΩ Sense Resistors
R(SNS) = 68mΩ
R(SNS) = 100mΩ
Output Inductor and Capacitance Selection Guidelines
The IC provides internal loop compensation. With this scheme, best stability occurs when LC resonant
frequency, fo, is approximately 40 kHz (20 kHz to 80 kHz). Equation 3 can be used to calculate the value of the
output inductor, LOUT, and output capacitor, COUT.
2p ´ LOUT ´ COUT
To reduce the output voltage ripple, a ceramic capacitor with the capacitance between 4.7 mF and 47 mF is
recommended for COUT, see the application section for components selection.
System Load After Sensing Resistor
One of the simpler high-efficiency topologies connects the system load directly across the battery pack, as
shown in Figure 35. The input voltage has been converted to a usable system voltage with good efficiency from
the input. When the input power is on, it supplies the system load and charges the battery pack at the same time.
When the input power is off, the battery pack powers the system directly.
Figure 35. System Load After Sensing Resistor
1. When the AC adapter is disconnected, the battery pack powers the system load with minimum power
dissipations. Consequently, the time that the system runs on the battery pack can be maximized.
2. It saves the external path selection components and offers a low-cost solution.
3. Dynamic power management (DPM) can be achieved. The total of the charge current and the system current
can be limited to a desired value by setting charge current value. When the system current increases, the
charge current drops by the same amount. As a result, no potential over-current or over-heating issues are
caused by excessive system load demand.
4. The total of the input current can be limited to a desired value by setting input current limit value. So USB
specifications can be met easily.
5. The supply voltage variation range for the system can be minimized.
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