Hi Team,
My customer design TPS62864 for 3.3V to 1.05V and 3.3V to 0.65V in his system, the performance is good but have a question about the switching frequency. Customer checked the spectrum then found there are two ripple frequency in output voltage rail. One is 2.4MHz, the other one is 2.6MHz. Customer doesn't understand how come 2.6MHz ripple appeared in output rail? Could team help comment it?
Thanks a lot.
Vincent Chen
Hi Dorian,
Sorry for late response.
Below is customer's SCH. The part number of output capacitor and inductor are 22uF/Murata GRM188B30J226MEA0 and 470nH/Murata DFE18SANR47MG0L. Customer measured the waveforms on his system, so the load is system load not a fixed load. System changed the device to FPWM mode after power up for getting lower output ripple.
Thanks a lot.
Vincent Chen
Hi Dorian,
Sorry for late response.
Below is customer's SCH. The part number of output capacitor and inductor are 22uF/Murata GRM188B30J226MEA0 and 470nH/Murata DFE18SANR47MG0L. Customer measured the waveforms on his system, so the load is system load not a fixed load. System changed the device to FPWM mode after power up for getting lower output ripple.
Thanks a lot.
Vincent Chen
Hello Vincent,
I would suggest, in order to minimize 2.6 MHz peak to use specific capacitor value too filter those:
It can also be improved by making sure the layout is done according to Guidelines and Example like in d/s.
Using a different inductor value than the one recommended 0.24nH could imply that the system is operating at a slightly different frequency.
Does the customer see at this point an influence of this 2.6MHz in his system?
Thanks a lot!
Regards,
Dorian
Hi Dorian,
2.6MHz doesn't affect system performance, customer is just wondering why it appears another switching frequency out of the expected frequency of 2.4MHz. I found the different load current would affect switching frequency, is it possible the variant load current causes the two switching frequency?
Thanks a lot.
Vincent Chen
