9.2.1 Design Requirements

A solar panel with VOC = 6 V in direct sunlight and capable of up to 1 W of output power is available to charge a 500 mAHr LiIon battery at a 1C rate. Because the light itensity will vary over time, this application uses the IC in battery tracking mode. The IC will never use load mode so EN is tied to PG.

9.2.2 Detailed Design Procedure

The minimum recommend capacitors of 1 µF for VBUS and BAT are used. The pullup resistors for CHG and PG are 2 kΩ.

Using R_ISET = K_ISET / I_OUT and set I_OUT = IC = 500mA gives R_ISET = 390 AΩ / 500 mA = 780 Ω → 787 Ω closest 1% resistor.

Using Equation 3 and finding RTH(45) from the 103AT-4 thermistor datasheet as 4911 Ω, RT1 = 1 / (0.186) * 4911 Ω - 4911 Ω = 21.492 kΩ → 21.5 kΩ closest 1% resistor.

For battery tracking mode, we leave VDPM floating. If we decided to power the charger using a 5-V wall adapter that a minimum output voltage of 4.6 V, we would size a resistor VDPM to ground using R_VDPM = (VBUS_{_DPM} – VBUS_{_DPM_1})/KVBUS_{_DPM}= (4.6 V - 3.5 V) / ( 0.15 V/kΩ) = 7.333 kΩ → 7.32 kΩ closest 1% resistor.

9.2.3 Application Curves

Figure 14. Accelerated Charge Cycle Using Solar Panel Input Source

Figure 15. Power Up / Power Down