I am working on a project where I have used MC-34063 boost supply on 3 pcb's and all the 3 places I have the same issue ie
- output voltage is steady on open circuit, but soon as ANY load is connected, MC starts drawing massive amount of current, and puts the Bench Supply from CV to CC mode. (it goes upto 1.5amp)
I am not sure what is the issue here as I have taken care of these precautions
- 4 layer board
- consistent ground plane
- very small ground loop for any return paths
- 100-150 mohm ESR caps and inductors
I am really clueless as to why the voltage is sagging, in all cases when I boost voltage from either 3.3v to 12 or 5v to 12v.
Current requirements in either case is less than 100mA and inductor is rated for 1.8amp.
if it helps, what I have noticed is disconnecting the 180ohm/drive resistor even though there is no boost, but there is no huge current consumption either!
Additionally, I tried
- changing drive resistor to lower values of 10ohm and higher values of 1kohms
- adding more capacitors at output
- added additional LC filter at output
Please see below for circuit daigram, layout and pcb pictures.
lastly please note, all the schematics, layouts and PCB's are pretty similar for both 5V and 12v, except for
- feedback resistors (1k, 9K) for 12V, and (1k, 3K) for 5v and
- output capacitors ratings of 10V for 5v boost, and 16V for 12v Boost