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MT3608 going wild
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fabiodl:
On a board I need 15.5V, that I generate from the USB bus.
In a previous revision I used a MT3608 module.
In this revision I integrated the chip on my board, and at a 40mA draw the noise is way worse than with the module (Vpp in the order over 1 V).
I used
this inductor    SRR1050A-220Y

this diode SS34FA

these caps C3216X5R1V226M160AC

and the layout is the one in the image.R23=82K, R24=3K3, RV1 is not installed.
Is there anything wrong in the components choice or the board layout?
fabiodl:
Here is a pic of the oscilloscope trace (infinite persistence enabled)
I also tried moving R23 next to the chip (I soldered it between R24 and C13) and it made no difference whatsoever
awallin:
without persistence-mode, is that a switching-glitch at ~1.1 MHz?
I guess that is expected and only goes away with more LC filtering on the output?
(you could try to probe the +5VDC input and see how that looks. more input capacitance might help?)
fabiodl:
awallin, thank you, I suspected that too ( the padauk free programmer seems to have a 47 uF output cap) so I checked the module I have.
It is even less. Both input and output are 7uF (maybe that's a low 10uF?)
I started replacing my parts with the module ones, in the following order

output cap-> no change
diode -> no change
inductor-> bingo!
now I will try to restore my output cap and diode and more importantly I need to understand why mine was unsuited and
fabiodl:

--- Quote from: blueskull on May 21, 2020, 08:59:28 am ---Check your inductor or IC soldering. Some boost converters are so amazing that they might be able to work from just stray inductance when the proper inductor is accidentally shorted, just with much higher noise and quiescent current. I had that mistake done on TPS61170.

--- End quote ---

I will test the inductor and try to resolder it, thanks for the tip!
edit: the inductor measures 20uH, 0.4ohm
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