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Published 20 hours ago • verified publisher icon Jana-Marie

Issues with Lenovo 4X20M26272 65w USB-C charger

Open jeanthom opened this issue 3 years ago • 4 comments

Hi,

I noticed a common issue among USB-C peripherals that are connected to this very specific model of charger: you can hear a faint whine noise, and there is a 1V ripple on VBUS (I'm probing C24 in AC mode in the picture below):

96366447-f5419c00-1147-11eb-8892-2d91300efe57

This is due to a too big capacitance on VBUS (USB spec specifies max 10µF). I remember fixing an FPGA board with a fat ass inductor but I'm not sure that this is a good solution.

This might explain the issues I'm facing in #8

jeanthom avatar Oct 18 '20 12:10 jeanthom

Hey, I tried to replicate that and indeed it seems to be the same with my Lenovo 65W PD supply, but also my other supplies. This is a problem that needs to be fixed. Thank you for bringing this to my attention :)

Jana-Marie avatar Oct 18 '20 18:10 Jana-Marie

Did you capture that trace with or without the tip connected/on?

hannesweisbach avatar Oct 20 '20 17:10 hannesweisbach

With the tip on. When I disconnect the handle I don't have such oscillations.

jeanthom avatar Oct 20 '20 21:10 jeanthom

Ok.

If I see that right, the oszillations have a frequency of rougly 3 kHz. Does that track with the PWM frequency of the otter iron?

hannesweisbach avatar Oct 20 '20 21:10 hannesweisbach