PSE and PD test fixture problem

Jacky Chen29

Genius 4735 points

Other Parts Discussed in Thread: TPS23754, TPS2378

Hola,

We want to modify our TPS23754 circuit for PSE function test purpose and the schematic that we modified as below：

Before modify：

POE_PD.pdf

After modified：

POE_PD_TPS23754.pdf

But we met a problem is that the TPS23754 will be burned down when PSE power source plug on！Does the schematic correct that I had modified？

Or it must be connected second side transformer？please help comment of this？Thank you ～

over 8 years ago

0 Darwin Fernandez over 8 years ago

TI__Mastermind 40790 points

Hi Jacky,

I'm not sure about the modified circuit. What is the overall goal for this mod? Is it to only test the PD functionality and not test the PWM design so you're adding the dummy load to imitate the converter? Please let us know. Thanks!

0 Jacky Chen29 over 8 years ago in reply to Darwin Fernandez

Genius 4735 points

Hola Darwin,

Thank you for your prompt reply. Yes, you are right. It is just test PD functionality not test the PWM design so I moved second side SR circuit

and adding the dummy load to imitate the converter.

0 Jacky Chen29 over 8 years ago in reply to Jacky Chen29

Genius 4735 points

Hola Darwin,

Below is our modified circuit for PSE load test use, do you have any comment of it？Thank you ～

POE_PD_TPS23754_Load.pdf

0 Jacky Chen29 over 8 years ago in reply to Jacky Chen29

Genius 4735 points

Hola,
Can someone help to reply this question？ Thanks ～

0 Darwin Fernandez over 8 years ago in reply to Jacky Chen29

TI__Mastermind 40790 points

Hi Jacky, since you're only testing PoE PD and not PWM controller, I recommend you only have to power VDD and not VDD1 and not include the PWM components. What is Q10 doing? I believe the internal FET of the IC should be okay.

You can also consider a PD only IC (no PWM controller) like TPS2378.

0 Jacky Chen29 over 8 years ago in reply to Darwin Fernandez

Genius 4735 points

Hola Darwin,

Thank you for the prompt reply. Because I need the power of 12V or 5V to control the Q10's output so I also need the PWM function with VDD1.

About Q10 is for protect internal MOSFET because of it will have a transient issue when maximum load current occurred so I adding one more power

stage to delay the current or TPS23754 will starting heating and only provide 7.5W！

0 Darwin Fernandez over 8 years ago in reply to Jacky Chen29

TI__Mastermind 40790 points

Hi Jacky,

VDD1 powers VC for a certain amount of time just to have some energy to begin switching so that a bias power (like from a bias winding of the power transformer) can power VC. The way it's designed now, when VC reaches it's rising UVLO, the internal regulator will turn off and since there is no aux bias power, VC will not be able to power anything. This is how a typical PWM controller works. Rather than using VC, you will need some external power source to bias your external circuitry.

0 Jacky Chen29 over 8 years ago in reply to Darwin Fernandez

Genius 4735 points

Hola Darwin,

Thank you very so much.

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PSE and PD test fixture problem