TPS23753A: Inrush current when hot-plugging adapters

Ryu Yamashita

Part Number: TPS23753A
Other Parts Discussed in Thread: TPS23730

Tool/software:

Hi team,

The following application note states that it is generally not a problem to hot plug an adapter with power on and excessive inrush current flowing through it.

https://www.ti.com/jp/lit/an/slva306a/slva306a.pdf

Why is this not a problem?
Also, in my experiment, an inrush current of 100A flowed.
The EVM diodes are rated at 50A and I am wondering if this could be a problem.
I would like to know if the “no issue” in the application note means that it will not break as a PoE IC, or if the diode is attached correctly, it will not be a problem.

Best Regards,
Ryu.

11 months ago

0 Diang Xing 11 months ago

TI__Mastermind 37121 points

Hi Ryu

Thanks for reaching out! I will take a look for your question and get back to you in 5 business days.

Best regards,

Diang

0 Ryu Yamashita 11 months ago in reply to Diang Xing

Genius 3725 points

Hi Diang,

Thanks for the reply.
I am in a bit of a hurry so I am waiting for your reply as soon as possible.

Best Regards,
Ryu.

+1 Diang Xing 11 months ago in reply to Ryu Yamashita

TI__Mastermind 37121 points

Hi Ryu,

The PCB copper thickness and components selections will make impact. Most of caps can handle a high transient current by the way. You can have some line inductor to reduce the peak current.

After add a 10uH inductor.

Best regards,

Diang

0 Ryu Yamashita 11 months ago in reply to Diang Xing

Genius 3725 points

Hi Diang,

Thanks for the reply.

Ryu Yamashita said:
I would like to know if the “no issue” in the application note means that it will not break as a PoE IC, or if the diode is attached correctly, it will not be a problem.

Does this mean that the diode can flow about 100A without any problem or damage to the PoEIC?

Best Regards,
Ryu.

+1 Diang Xing 11 months ago in reply to Ryu Yamashita

TI__Mastermind 37121 points

Hi Ryu,

Thanks for your reply.

It depends on the diode's electric characteristics. A 3 A rated diode could have 100A Non-Repetitive Peak Forward Surge Current 8.3ms as below example. Besides, in real cases the electron/hole carriers inside semiconductors may saturate and has a lower peak current than SPICE model based simulation too.

Best regards,

Diang

0 Ryu Yamashita 10 months ago in reply to Diang Xing

Genius 3725 points

Hi Diang,

Thanks for the reply.
I understand now.
Please let me know one additional point.
I have set the class detection resistor of the TPS23730 to operate as IEEE802.3bt Class6
If the PSE side negotiates with 2-pair as IEEE802.3bt when the class detection resistor of TPS23730 is set to operate as IEEE802.3bt Class6, is it not possible to negotiate?

With the above class setting, PSE supporting IEEE802.3at can negotiate with no problem.
However, when an extender that may be operating in 2-pair mode as IEEE802.3bt is inserted between PSE and PD, TPS23730 cannot negotiate.

Best Regards,
Ryu.

0 Diang Xing 10 months ago in reply to Ryu Yamashita

TI__Mastermind 37121 points

Hi Ryu,

PoE team is out of office and will be back on next Tuesday. Please expect a delayed response and thanks for your patience.

Best regards,

Diang

0 Ryu Yamashita 10 months ago in reply to Diang Xing

Genius 3725 points

Hi Diang,

What is the status of this case?

Best Regards,
Ryu.

0 Diang Xing 10 months ago in reply to Ryu Yamashita

TI__Mastermind 37121 points

Hi Ryu,

Theoretically a standard BT PSE should be able to handshake and run into a power demotion mode. Could you let me know which BT PSE you used?

See the links below about power demotion:

https://www.ti.com/video/5786317242001

e2e.ti.com/.../faq-poe-understanding-power-demotion

Best regards,

Diang

0 Ryu Yamashita 10 months ago in reply to Diang Xing

Genius 3725 points

Hi Diang,

Thanks for the reply.
I understand now.
After verification, I suspect a problem with the extender, but I will send you the parts used just to be sure.

Extender: DEPX-G3BTS (Diatrend)
PSE: TL-POE170S (tp-link), PD-9601GC/AC (Microsemi)

Best Regards,
Ryu.

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TPS23753A: Inrush current when hot-plugging adapters