Liam Lynch

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

10 years, 10 months ago.

Low 3.3V out on P3V3 on the FRDM-KL25Z board?

Hi,

I an totally new to the KL25Z board and experimenting with it as an alternative/upgrade to the good old Arduino.

I noticed on a blog a report that the 3.3 volt output on pins (4 & 8) P3V3 is faulty, providing very low current. Just measureing my board revealled it is outputing 2.9V unloaded on my DVM. My board is a rev D I think.

This is going to prove a problem if unnoticed. Is there a proper fix for this?

Regards

Liam

3 Answers

Liam Lynch
poster
10 years, 10 months ago.

Hi,

Thanks for the answer, and I'll do some more tests.

That kind of voltage drop could be a bit of an issue for some sensors. Maybe need to make a breakable link here.

That link that o truyen posted, seems to be a bit lanuage specific..

Regards

Liam

Accepted Answer

I expect the vast majority of the boards to be fine with it. Although of course it is a risk, especially if a board also has a similar setup, then you have 2 diodes in series, so double the voltage drop. But in principle every IC normally is already rated to operate nominally at -10% Vdd.

posted by Erik - 24 Jun 2013

Well I'm getting about 2.9V on the P3V3 pin. This is worse than -10% which would be 2.97V. The problem I have is that I want to communicate with a Nintendo Classic Controller and all the information I have on that simply states that it needs a 3.3V supply. I think I will short out the diode since I really need to be sure the supply is good before tackling other problems. The other board I want to talk to is the Gameduino shield. This needs 2 supplies : one in the range to 3 to 5V and the other 3.3V. So a 2.9V supply really won't cut it (although I admit I haven't actually tried it).

posted by Richard Ellingworth 26 Jun 2013
Erik -
10 years, 10 months ago.

A quick check of the schematics show the issue is the coin cell: It can either be powered from the coin cell or from a voltage regulator, and to combine them there are two diodes. This shouldn't mean they provide low current, but it does mean there always will be a voltage drop over the diode.

Doesn't this seriously compromise the board's compatability with Arduino shields? Some shields expect a good 3.3V supply and given the maximum voltage drop across the diode is 0.4V they could be getting as little as 2.9V. Not good.

posted by Richard Ellingworth 24 Jun 2013
o truyen
10 years, 10 months ago.

you can view http://otruyen.mobi/