MC34063 Regulator (MP3 Player Charger Circuit)-Output Current

Condition: It is a MP3 player charger circuit. The MP3 player charger is replaced 10 ohm load for hardware testing. However only output voltage reaches 4.46 V (5 V for actual value), while [b]the output current only becomes nearly zero[/b]. The maximum output current should reach 660 mA in order to charge the MP3. The circuit is [b]only able to charge a wireless modem but not MP3[/b].

MC34063 only can operate when its [b]5th pin and 4th pin exchange their connections[/b].
Thus, what should i do to enable the circuit to charge MP3?

The MC34063 buck regulator you show is set to current limit at 900 mA. The oscillator frequency is set between 51 and 88 kHz. At 51 kHz the inductor current reaches 750 mA and the circuit should be able to supply 660 mA at 5 volts.

However, the inductance of the 220 uH inductor will decrease with increasing current and if it drops too much the current will exceed the 0.9 amp limit.

You might try increasing the current limit by paralleling one more 1 ohm resistor across the current sense resistor. Another thing to try is to increase the oscillator frequency by replacing the 470 pF cap with a 390 pF cap. This will reduce the peak switch current. And if the inductor is being driven into saturation it will need to be improved.