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Topic: Defect in the Arduino Micro Board design , Please help (Read 331 times) previous topic - next topic

bemin

HI Arduino,

This question is for the people who really understand Electronics.

I am using the Arduino Micro for a project and I noticed the following concern , please correct me if i am wrong, there is two options to power on the board

1- External Power supply. The Board uses the LP2985- 33DBVR voltage regulator to regulate the Vin to +5 V
2- It uses the USB +5 V input to power on the board instead of the power supply.

Now the problem I noticed happens when the USB is used to power on the board. The VUSB is connected to the +5V which is connected to the Regulator output. That means when using the USB as a power source the Regulator output is 5v and the regulator input is 0V.  Is that going to cause any issue in the future for long term use?

After reviewing the Regulator datasheet it says that if the Vout is higher than the Vin this cause a diode forward biased and cause a parasitic silicon-controlled rectifier to latch , resulting in a high current  to flow from the output to the input , and it is recommended to connect a Schottky diode between the regulator Vout and Vin  to prevent  damage the regulator.

I don't see any thing mentioned about the Schottky diode on the ardunio micro datasheet , pin diagram or circuit diagram.


Can you please let me know if they already fixed this problem or no ?

if no, Who should I contact , If I would like to order few hindered boards with the modified design -adding the schottky  ?

justjohn

But the regulator input isn't less than the output unless it's connected to a supply that's less than 5 volt, or to ground, which it shouldn't be.

Grumpy_Mike

Some people wire up the Vin to 5V if this is a concern to them.
Otherwise in prictice this i has not been found to be an issue.

People do bring this up every now and then.

tinman13kup

Quote
The Board uses the LP2985- 33DBVR voltage regulator to regulate the Vin to +5 V
No, that is the 3.3V regulator that takes either the USB input OR input from the NCP1117-5 and regulates it down to 3.3V.

The NCP1117-5 is the 5V regulator.
Tom
It's not a hobby if you're not having fun doing it. Step back and breathe

pert

Also posted at:
https://github.com/arduino/Arduino/issues/7016
If you're going to do that then please be considerate enough to add links to the other places you cross posted. This will let us avoid wasting time due to duplicate effort and also help others who have the same questions and find your post to discover all the relevant information. When you post links please always use the chain links icon on the toolbar to make them clickable.

bemin


Grumpy_Mike

Yes post with no answer at github.com
So care to comment on the answers you got here?

justjohn

So care to comment on the answers you got here?
ha, ha. "grumpy" but "logical" - not so much as any acknowledgements, thank-you's or anything.

bemin

regardlessss

this issue has been resolved, I found out the following .
1- yes when you use the USB there is +5V on the regulator output pin
2- yes your Vin has no voltage and it is grounded with a capacitance
3- Yes the Vout voltage is higher than the Vin voltage , and current may flow

However, that is all been said, the regulator that is used to regulate to + 5V has a two protection Diode that will protect the regulator for this specific problem.

Thanks Guysssss !!!!!!!!!!!!! :D :D

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