LM5071: Can the LM5071 handle boosting?

Brian McKee

Part Number: LM5071
Other Parts Discussed in Thread: PMP22301

I'm adding dual ethernet to an existing product. POE is one of the design requirements.

The system is typically powered by 24 VDC (wall wart or similar). Total system power is no more than 8 watts.

The first search result I got was the LM5071 which is a good solution because it allows the system to be isolated from either POE or from an external DC supply, enabling customers to choose the power source (another design requirement)

But this raises a couple of questions.

Examples show 3.3 V and 5 V, but nothing higher. There doesn't seem to be a max specification for Vout. Is it okay for the output of the transformer to be 24 Volts?

Can the LM5071 handle 24V to 24V buck / boost operation from an external supply?

Thanks in advance.

8 months ago

0 Diang Xing 8 months ago

TI__Mastermind 27481 points

Hi Brian,

Thanks for reaching out.

AN-1430 is LM5071 based 3.3 V flyback converter reference design. You could consider to modify its secondary side circuit to change the output to 24V.

PMP22301 is a 24-V flyback reference design, you may consider to use PMP22301's parameters to adjust the LM5071 secondary side circuit.

Best regards,

Diang

0 Brian McKee 8 months ago in reply to Diang Xing

Prodigy 30 points

Thanks Diang.

That answers my first question. How about the second question:

Can the 24V output of the LM5071 use 24 V input from an external supply? In other words, can the LM5071 do a buck boost configuration?

Brian

0 Diang Xing 8 months ago in reply to Brian McKee

TI__Mastermind 27481 points

Hi Brain,

Thanks for your reply. Do you want to have the DC adapter on the secondary side? You can oring the 24V DC with the 24V PoE output with an oring diode like the blow Option3 position.

More oring circuit information you can check in www.ti.com/.../slva306a.pdf

Best regards,

Diang

0 Brian McKee 8 months ago in reply to Diang Xing

Prodigy 30 points

Thanks. The answer is: the DC to DC controller in the LM5071 is buck only. That's what I was looking for. Thanks.

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LM5071: Can the LM5071 handle boosting?