Overheating mc34063 as boost converter
I've been using the mc34063 in boost converter manner to build an external battery circuit for 3.7v->5v DC-DC conversion, but within few minutes of operation the chip and the inductor begin to overheat beyond touchable (light smell of burning components too), occurring with both circuits that I had. I've tested using the following devices: ipod touch 2G, ipod touch 5G, kross g6 tablet, all of which had the circuit overheat. The power source is 4 cylindrical cells in parallel @ 3.8v ~9A with protection circuit. The batteries do not overheat and I'm guessing the protection circuit regulates the current to an extent. I've tested the current draw of the ipod 5G to 100mA while the circuit is wired for 500mA. This is what the schematic looks like: http://www.eeworld.com.cn/uploadfile/dygl//201210/20121025102243965.png
I would like some help in troubleshooting the overheating of the circuit, Thank you.