PTN78020HAH in parallel connection

John Tzortzis

Other Parts Discussed in Thread: PTN78020H

Hi there,

I 'm member of a university team and we are trying to build a charging system for supercapacitors. So we use three PTN78020HAH in parallel connection each of them has an adjusted output on 15V. Two months ago one of the buck converters was burned during our test. After debugging the whole system we discovered that the burned PTN78020HAH has a little higher output voltage(0.2V-0.4V) than the others so it was working more than them.

After that, we replaced the adjustment resistors needed with new that have tolerance 0.1% as mentioned in the manual. Then, two buck-converters have output voltage 14,98V and the third 15,01. We guessed that it was a very little difference and started the tests again. Unfortunatelly after some tests, that buck converter got burned again.

Is that little voltage difference responsible for this or it is our mistake? And if yes, could we use just one resistor for the three buck converters(they have common ground) to have the exact same output?

Thank you in advance,

John

over 9 years ago

0 JohnTucker over 9 years ago

TI__Guru**** 191445 points

In general these are not designed for parallel operation. Usually you will want to use a multiphase circuit or just a converter designed for your maximum current. There are quite a few converters that can output 20A or more. What are your specific requirements?

0 Tom Guerin over 9 years ago

TI__Mastermind 38230 points

John:

The PTN78020HAH is not designed for parallel operation. The units wil lcontinue to be overstessed and fail.

There is no method for paralleling these modules. I recommend you search for this on the TI WEB site for discrete solution .

Tom

0 JohnTucker over 9 years ago in reply to Tom Guerin

TI__Guru**** 191445 points

Yes , thats what I said. We need tofind their requirements and point them in teh right direction. Thanks.

0 John Tzortzis over 9 years ago

Prodigy 90 points

Thank you for your fast responses.
The requirements of our system are: max output 20A or more and max input voltage 35V.

John

0 JohnTucker over 9 years ago in reply to John Tzortzis

TI__Guru**** 191445 points

And output voltage = 15V?

0 John Tzortzis over 9 years ago in reply to JohnTucker

Prodigy 90 points

Excuse me! Yes 15V output.

0 JohnTucker over 9 years ago in reply to JohnTucker

TI__Guru**** 191445 points

You could look at possible solutions here:
www.ti.com/.../step-down-buck-controller-products.page;100&p32=1;1&p451max=20;20

0 John Tzortzis over 9 years ago in reply to JohnTucker

Prodigy 90 points

bucks_connections.pdfWe are looking for a fast solution to our problem so we just came up with a new design. We cannot afford to burn any more PTNs and that's why i sent you the schematics before the implementation.

In the attached file, circuit 1 is what we currently have. Circuit 2 is what we thought will work. In our new design (circuit 2), each buck converter will charge one cap so it doesn't matter if they don't have exactly the same output voltage. The current will flow from our source to both the converters, so they will both work and none of them will get burnt.

How do you think of this possible solution?

Thank you

0 JohnTucker over 9 years ago in reply to John Tzortzis

TI__Guru**** 191445 points

Please try to re attach your schematics...

0 Tom Guerin over 9 years ago in reply to John Tzortzis

TI__Mastermind 38230 points

John:

I do not see any attachment in this TI format question.
Tom

0 John Tzortzis over 9 years ago in reply to Tom Guerin

Prodigy 90 points

Sorry, i attached the file.

1462.bucks_connections.pdf

0 Tom Guerin over 9 years ago in reply to John Tzortzis

TI__Mastermind 38230 points

John:

I reviewed the Oring diode and it may work , not ideal current sharing ,if the diode forward voltage(Vf) has a wide range over temperature. One PTN78020H will be the major current source until the diode VF increases with temperature.

Tom

0 JohnTucker over 9 years ago in reply to Tom Guerin

TI__Guru**** 191445 points

Tom, if you are good with it then it should be settled. Thanks.

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PTN78020HAH in parallel connection