1 - SMAT - Positive terminal connected to solar cells
2 - BAT - Rechargeable battery positive terminal connection
3 - VCC - Ground
4 - LX - Power switch drain
5252F does several things:
It charges the 1.2v battery during the day, using power from the solar cell.
It detects when is dark (when the solar cell is in dark) and turns LEDs on. And turns LED off when is enough light.
It boosts the 1.2v from the battery to over 3v.
We can control how much current (mA) it gives out by choosing different values for the inductor (L1).
Without a solar cell, it works like a Joule thief.