Part Number:TPS630242
Hi Team,
Good morning, my customer is using the TPS630242 in their design and seeing a lot of noise on the output:
The ripple is about 9-11mV and there is a 60 kHz sub-harmonic oscillation. I haven’t looked at the inductor current which would tell me if indeed these are sub-harmonic oscillations.
Attached are some scope captures where I measured the ripple at the output filter caps, no load. I set the PFM/PWM pin low and then high and initially didn’t see any difference in the waveforms. I then changed the inductor value to a 4.7uH and the converter did not like this. I was seeing 0.5A drawn from the input continuously. I then replaced back the original 1uH inductor and measured the ripple again. This time, the PFM/PWM pin did place the IC in PFM mode when low and in PWM mode when high. However, the sub-harmonic oscillations are there.
No Load Forced PWM:
No Load PFM:
After Inductor Change:
Interested for your thoughts and please let me know if there are any questions.
Regards,
~John