soldering mk20 mk22 - power test problem

Werner Almesberger werner at almesberger.net
Tue Sep 1 05:51:14 UTC 2015


Rafael Ignacio Zurita wrote:
> No yet. There is not connection between vout33 and vdd.
> I wanted to check the vout33 first, before to do those connections.

If you want to play it extra-safe, you could power VDD from a lab
supply and power 5 V from USB (or another lab supply, if you have
one). With VDD powered, the system will be in a defined state.
Then the regulator has no excuse for not working :)

But I wouldn't worry about VDD possibly getting a bit too high,
and just make sure the system can't burn too much power. See
below.

>> Also, the regulator may need a minimum
>> external load of a few uA before it actually can regulate.
> 
> It does not. At least when checking with tester.

Hmm, the tester may not provide enough of a load. If things
still don't work after powering VDD, maybe add some 1-100 kOhm
resistor between VOUT33 and GND.

> usb port and using 5v from a pc power supply.

For such things, I'd strongly suggest to use a lab supply. If you
set a low current limit (e.g., 20-50 mA), there is little risk of
anything getting damaged, even if you made some bad mistake.

Up to a certain point, a low current limit also helps to prevent
damage if you run with an incorrect (or reversed) voltage.

If you're working with a supply that can provide several ampere,
you can easily burn up your circuit if something isn't quite
right.

- Werner



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