Hello,
Schematic is attached.
Input ranges from 8-18V, output load is 80 - 120 mA at 15V.
When powering up enabled the output has a large ripple (2.75Vpp at about 406Hz).
When powering up disabled (P28 shorted) then enabling by removing shunt from P28 the output is OK.
Any ideas?
Hi David,
Apologies for the delayed response.
Would you mind going into more detail on the exact test condition for both cases?
Are you testing with input as power supply? If not, what are you using to supply input?
Do you have any waveforms you can share?
Best Regards,
Yu
Hi David, did you get this sorted?
I’m experiencing something similar at different voltage and current ranges.
Hi Yu,
I need some help with similar behaviour happening in my design and also with the MPS28167-A Demo Board.
Powering from 3 or 4 AA cells with the output set to 5V with a load of 22 to 33ohm and a capacitance of about 200uF, when the battery voltage gets down to about 3.9V there is a large ripple on the output it gradually increases to about 1V at 3.8KHz at around 3.75V input then as the battery voltage goes down even further it gradually decrees and ceases about 3.1V and never comes back then the regulator shuts down at about 2.6V.
I also tried powering the circuit with a 5A bench power supply and it does the same at the same input voltage range. please note that this also happens with the MPS28167-A Demo Board.
Soft start is functioning in one of the cases and not in the other. I would be tempted to put a giant electrolytic cap on the output to see what happens 500uF or so
I’m not sure how soft start could be the problem because this doesn’t happen at start I have the regulator on at 5 V input and everything is OK, then I start reducing the input voltage slowly 10mV at a time and the ripple appears at around 3.9V increases as I reduce the input voltage to 3.75V and the ripple starts decreasing as I reduce the voltage further to 3.1V then it disappears at lower voltages. I reduced the output capacitance to 10uF and it improved, but I need about 186uF in the final application. I will try higher output capacitance too.