Hello,
We have been using the LM2575S-3.3 device in some of our designs for some time without issue. Normally we get a small ripple voltage of approximately 10-15mV (pk-pk).
Recently we have had issue with parts coming from our manufacturer, some of the boards would exhibit much higher ripple voltage (70-100mV pk-pk). This has a large effect on our application since we use ADC's and use the 3.3V line as a reference. Through removing and swapping components one at a time we found the buck converter itself was the cause of this large variation. The ripple can be smoothed by a larger output capacitor, we normally use 330uF but smoothing the higher ripple buck converters takes about 800uF.
We also did a batch test and found that while 70% of the devices coming from our manufacturer had this issue, none of the 10 devices we tested when purchased from a distributor had the issue.
Is this likely to be a tolerance issue in the part? An increase of approximately 8 fold in ripple voltage seems an awful lot when all other factors are identical. Or have we been unlucky and gotten a faulty batch somehow?
The date/batch code on the 'faulty' devices are:
41AY9T0E3