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TPS23753: Advanced Adapter ORing Solutions using the TPS23753

J
Expert 1055 points
Part Number: TPS23753
Other Parts Discussed in Thread: TPS23730, PMP20859

Hi 
I would like to use Adapter ORing and I read the Advanced Adapter ORing Solutions using the TPS23753.

According to this document, I have some questions I'd like to ask.

1.) On page 2 .The ability to disable the internal hotswap MOSFET is necessary for both option 2 and 3 adapter preference configurations while the independent VDD1 pin simplifies PoE preference configuration for option 2. what does this sentence mean?

2.) If I have two input connections one is PoE the other is an adapter, it is necessary to use APD pin, what happens if I don't use APD pin.

3.)The APD pin and DEN pin both can use to disable the hotswap why I can just use DEN pin?

4.) for option 2 case, why APD > 1.5V, Vdd connected to Vdd1, which mean the diode between the Vdd and Vdd1 conduct?

5.) Why option 1, option 2, and option 3 should use different grounds? Option 1 use Vss, Option 2 use RTN, Option 3 use DC/DC converter ground.

6.) In section 3.3, If the PD is operating from PoE power before a live adapter is inserted, the internal hot-swap MOSFET opens, forcing power to come from the adapter. what does this sentence mean?

7.) In what situation do I need to put APD pin to RTN pin?

8.)What's is the best choice between adapter ORing and Power Mux?

  • 0
    TI__Mastermind 21320 points

    Hello, 

    Overall, I suggest closely copying a reference design that meets your needs. Let us know if you need help selecting a reference design or EVM to base your design on. 

    1. There is an internal hotswap MOSFET that connects VSS and RTN inside all TI PoE PD IC's. If you want the adapter to be priority, aka if the adapter and PoE are plugged in at the same time the adapter will be prioritized to power the load, then disabling this internal hotswap MOSFET is very important for adapters configured in option 2 or 3. 

    If you want PoE to be prioritized, VDD1 makes this easy (simplified). 

    2. If it is not used, APD will not be prioritized. You need to choose if PoE or APD will be prioritized, choose the adapter voltage level (48V will be option 2, 12V/5V will be option 3), and then follow the Application note for implementation. 

    3. You can use the DEN pin you just have to be careful with the divider chosen and the current it will create through the optocoupler. This results in more parts and more calculations, but you are welcome to do it this way. That is why we specified how to do it. 

    4. For option 2, APD is grounded if there is a diode between VDD_VDD1 and if APD is raised above it's threshold there is no diode between the VDD_VDD1. 

    APD gives adapter priority. 

    Grounding APD and connecting a diode between VDD and VDD1 gives PoE priority. 

    Do not do both. 

    5. yes that is the distinction. 

    6. it means that internal hotswap FET discussed early opens. AKA the FET turns off. Therefore VSS and RTN are no longer connect, therefore the PoE cannot power the DCDC. The power must come from the adapter. 

    7. This is discussed at length in the paper. One example is when Option 2 PoE priority. 

    8. I cannot tell you what the "best choice" is. Typically, a 48V adapter is option 2. A 12V adapter is option 3 with diodes. A 5V adapter is option 3 with a power MUX. This is typical design choices at a very high level. 

    As discussed earlier, I strongly  encourage you to review our EVM and TI Reference design portfolio. The TPS23753 has the most reference designs out of any of our parts. I would encourage you to find a refence design that meets your output voltage/power level needs and to order said reference design. We provide test reports, but you can also test it to understand how it works. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Expert 1055 points

    Hi 
    I'd like to use TPS23730 and the output is 5V and also have an adapter ORing function, but I am not very understand how Option 1, 2, 3 work. although I read the document,
    and Thanks for your answer and I have some confusing things.

     1.) I do not understand why should I need to disable the hotswap, what happens when I use PoE and adapter and then connect the hotswap?base on your previous explanation, at first the PoE needs to detect so it needs to disconnect the hotswap, after classification the hotswap connects so VSS connects to the RTN. but in this case, why need to disconnect the hotswap, I am very confused.

    2.) If I ground the APD pin, which means I cannot disable the hotswap, is it OK?

    3.) If I raised the APD above the threshold which means the priority is Adapter?

    4.) What situation I can use Option 1, in your reply 48V for option 2, 12V for option 3, 5V for Power Mux..

    5.)What's the consideration to choose Power Mux or adapter ORing.

    I have read some reference designs and documents because of the Covid 19 I cannot go to lab to test, sorry about that I have too much questions.

  • 0 in reply to J
    TI__Mastermind 21320 points

    Hey Jack, 

    The TPS23730 has a 5V  / 50W reference design : https://www.ti.com/tool/TIDA-050045 

    1. the hotswap is internal, so you are not connecting it or turning it on. The behavior will depend on how APD and DEN are configured. IN the reference design above, the adapter is connected to APD and therefore the hotswap FET will not turn on when PoE is connected. 

    2. That depends on what you want prioritized and how your adapter is connected. 

    3. Yes if adapter is connected to APD and APD goes above the threshold then the adapter is prioritized. 

    4. Do not use option 1 in your case. You do not need to. Option one uses the hotswap MOSFET to limit in-rush current on the adapter. This is a unique case and you do not need to use it. 

    5. The case is as I explained last time. the adapter voltage is the determining factor in most cases. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Expert 1055 points

    Hi Pahl
    Thanks for your kindly answer

    1.) TPS23730 doesn't have VDD1, if I'd like to use Option 2  PoE prioritized how should I do it.

    2.) Which case can I use option 1, I am curious about that.

    3.) Do you have hitless PoE? can you offer me some reference design and documents.

    4.) I'd like to know what's the difference between hitless PoE and redundant PoE, Do you have some material I can read?

  • +1 in reply to J
    TI__Mastermind 21320 points

    Hey Jack, 

    1. The previous design I sent has adapter priority with TPS23730 as does the EVM

    2. General – Requires 48-V, isolated output (from mains and ground) adapter • Benefits – Adapter inrush current is managed when the PoE source (PSE) is not present.

    3. This is in the app note: You must use "PoE Present" logic and a switch (or FET) to disconnect the adapter in this case

    4/5)

    PMP20859

    https://e2e.ti.com/blogs_/b/powerhouse/posts/delivering-a-smooth-transition-from-ac-to-poe-power 

    https://training.ti.com/designing-dual-input-poe-pd-systems-power-redundancy-smooth-transition-and-power-sharing

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Expert 1055 points

    Hi PahL

    Thanks for your kindly help.