Voltage Reporting problems

[tobias]

Hmm, I would have expected that but there is a possibility the spike might occure during power off. That might be a bit harder to test though. Maybe if you just set a trigger on e.g. 5V to let the scope detect a possible spike.

[omwdunkley]

Hmm, I would have expected that but there is a possibility the spike might occure during power off. That might be a bit harder to test though. Maybe if you just set a trigger on e.g. 5V to let the scope detect a possible spike.

I think i checked for that too ( different test setup, directly connected to the battery).

Ill test for shut down spikes thoroughly tomorrow.

I hope i find something; )

[tobias]

This is from the datasheet of the regulator but I don't think it is the problem, at least it shouldn't show up if you load VCOM as it is on the input side.

Regulator Protection
The TPS793xx PMOS-pass transistor has a built-in back diode that conducts reverse current when the input
voltage drops below the output voltage (for example, during power-down). Current is conducted from the output
to the input and is not internally limited. If extended reverse voltage operation is anticipated, external limiting
might be appropriate.
...

[SuperRoach]

I wonder if powering the regulator by itself may be needed due to the damage - power from an usb or arduino or something, and measure for on/off spikes there.

[tobias]

Can you both check the FB voltage on the damaged regulators as described here? That might give us a clue.

I wonder if powering the regulator by itself may be needed due to the damage

If there are no voltage spikes exceeding the maximum ratings of the vreg it shouldn't be needed.

[omwdunkley]

Measure 0.8V. Should be 1.22? I guess we found smth fishy
Also checked for shutdown spikes - couldnt find any.
If it helps I can send over one of the broken flies.

My new regulators just arrived - but Ill hold back on trying to replace them since I share the same symptoms as SuperRoach and replacing the the reg didnt help him.

[tobias]

Yes the reference should be 1.22V and by some strange reason it has broken.
I don't think sending one of the broken flies would help that much but instead I'll buy a step-up and see if I can reproduce it.

It is possible to use a fixed version (e.g. TPS79328 2.8V vreg) of the regulator as well as the feedback pin isn't connected on those, if for some reason that is the problem. If the USB isn't used a fixed 2.8V will work just fine. I'll see if I can get a hold of one of those as well.

[myrcfocus]

I have my FPV parts and regulator to solder onto my CF but am concerned about the best pins to use for power - can anyone please clarify which are the best to use?

Thanks!

[tobias]

You should connect it to VCOM and DGND. This might help explaining it a little as well.