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TPS2373: Reference Design for 12V Output

SUMIT RANJAN
Expert 2005 points
Part Number: TPS2373
Other Parts Discussed in Thread: PMP7499, TPS2379, PMP9256,

Hi Team,

I am planning to use TPS2373 for 60W deliverable. My output voltage requirement is 12V.

I got one EVM board reference design "SLUUBJ1A " but that is based on Maximum output voltage 5.5V. Please provide me any reference design for 12V output.

  • 0
    TI__Mastermind 40885 points
    Hi Sumit,

    I recommend using the same design on the EVM that you reference, and switch the converter design to the one used in PMP7499. Please see below link.

    http://www.ti.com/tool/PMP7499

    Thanks!
    Regards,
    Darwin
  • 0 in reply to Darwin Fernandez
    Expert 2005 points

    Hi Darwin

    Thanks for information.

    There is one confusion for me. Generally IEEE802.3bt is used for 60W deliverable but in reference design of PMP7499 , IC TP2379 which has been used that is IEEE802.3at.
    Which will be of 30W range.So how we are taking 12V@5A with TPS2379?

    Another point, If above point will be clarified then Can i use Oring with Adapter on output of PD controller that is at 12V@5A in this design?

    For Adapter ORing can i follow same application note  "SLVA306" which has been for TPS2373?

    Thanks & Regards

    Sumit Ranjan

  • 0 in reply to SUMIT RANJAN
    TI__Mastermind 40885 points
    Hi Sumit,

    Just to clarify, you can copy the same PD front end of the EVM from SLUUBJ1A with the TPS2373. Then replace the DCDC conveter (active clamp forward), with the DCDC converter in PMP7499. Then you would have a IEEE802.3bt controller paired with a converter that can do the 12V/5A that's needed for your application.

    For ORing solution, you can do ORing on the secondary like shown in the app note. Just note that since this is active clamp forward converter, you should have a diode after the converter design and a diode at the adapter so that when adapter is plugged in, the diode will block any back drive of the converter from the adapter. The opto circuit in the app note should also still be used to turn off the converter. For the TPS2373, be sure the auto MPS is functionality is not being used so that the PSE can remove power.
  • 0 in reply to Darwin Fernandez
    Expert 2005 points

    Hi Darwin,

    Thanks for detailed. Now everything is clear. 

    -------> Regarding diode for reverse protection, do we need to add diode on both point, that is on output of adapter as well as output of POE converter design?

    From Adapter side we will have12V. After the converter design of PD we will have transformer which will be isolated so if we will not provide diode after PD converter design and diode only at Adapter output then there will be any issue?

    Note: On Diode side we will have loss of power so can you please suggest any cheaper Ic for reverse protection with this much wattage (12V@5A).

    ------> For opto circuit yes i will use and will take care.

    -------> Regarding MPS, What will happen if we will keep option for automatic MPS control. Please clarify this.?

  • 0 in reply to SUMIT RANJAN
    TI__Mastermind 40885 points
    Hi Sumit,

    That's correct, there should be two diodes on the outputs of the adapter and the PoE converter.

    Yes there is a possibility that the adapter will be shorted by converter's synch driver circuit. If a diode is not desired, a series PFET can be used with the body diode blocking the adapter current. Then the gate can be pulled down with an NMOS driven. The gate of this NMOS can be driven by another NMOS (to help invert the logic) driven by the adapter voltage.

    After thinking about the auto MPS comment a bit more, it might not be a problem. The PD might hit current limit when the adapter is removed and PSE is connected, then converter might turn off for a short time while it's recharging the bulk cap. But I don't expect any damage.

    Regards,
    Darwin
  • 0 in reply to Darwin Fernandez
    Expert 2005 points

    Hi Darwin,

    Thanks for clarification. I will keep option with and without for MPS.

    Also i will open this ticket again for schematic review once i will update schematic.  Thanks for support.

  • 0 in reply to SUMIT RANJAN
    Intellectual 925 points

    Hi Team

    We are copying PD front end of the EVM from SLUUBJ1A with the TPS2373.Then replacing the DCDC converter (active clamp forward), with the DCDC converter in PMP7499 as per Darwin suggestion in the previous threads because we are going with 12V/5A power rating.

    The power flow diagram which we are going to use in our design is as below:

    Our Queries are as follow:

    Ques1: As LED driver input is connected to the output of bridge rectifier in PD controller. So we would like to know whether it can create a problem for PD detection or not(This will also act like Load).

    Ques2: As per PMP7499 (slvrb55) document can we provide 12-57VDC instead of 39-57VDC at J6 connector for 12V/5A circuit. If No, then what changes we have to do in that design to work for this much input voltage range.

  • 0 in reply to JASBEER SINGH
    Intellectual 925 points
    Hi Ti Team

    We are waiting for your valuable reply.
  • 0 in reply to JASBEER SINGH
    TI__Mastermind 40885 points
    Hi Jasbeer,

    1. The LED driver should be connected to VDD-RTN side of the PD controller. Otherwise, it could affect detection.

    2. PMP7499 was not designed for a 12V input. Rather, I recommend looking at the PMP9256 which has a wider input with the same output power requirements.
    www.ti.com/.../PMP9256
  • 0 in reply to Darwin Fernandez
    Intellectual 925 points
    Hi Darwin

    Your support is appreciable.

    We understood your points and now everythink is clear.
    We just want to know following points for the sake of our knowledge.

    1) If on power board DC jack connected and POE will not connect on control board and if we will follow option 1 of SLVA306A ORING document, so could we able to connect 12V and 24V adapter as well ?As per document only 48V adapter feasiblity is mentioned.

    Note: Our customer will not going to connect POE and Adapter both at same time.

    2) In datasheet of TPS2373 MPS duty cycle was mentioned. Could you please let us know how it will affect our design .


    If there is any confusion on my query then please let me know.
  • 0 in reply to JASBEER SINGH
    TI__Mastermind 40885 points
    Hi Jasbeer,

    1. The TPS2373 does not have an adjustable PoE UVLO. It expects a PoE input (between VDD-VSS) per the standard. This means 12/24V adapters will not work for option 1 with the TPS2373. It will work with a 48V adapter.
    12V and 24V can work for option 2 oring per the app note you reference with the TPS2373. The consideration will be that the converter should be designed for the wide input voltage range. In addition, UVLO_SEL should be chosen depending on the adapter voltage range.

    2. If using option 2, and adapter is providing power to the load, there will be little current through the PoE port. TPS2373 has automatic MPS in which it will provide the MPS current to keep the PSE connected during this condition. It can be disabled if necessary through AMPS_CTL
  • 0 in reply to Darwin Fernandez
    Expert 2005 points

    Hi Darwin

    Thanks for clarification.

    One small query i have from SLUUBJ1A ( TPS2373-4EVM-758). In this instead of using discrete diode for bridge rectifier we can use one ON-Semi Part having part number "FDMQ8205A"

    But this suggested part is complaint only for IEEE802.3at not for 802.3bt. So, I am in bit doubt whether we should use it or not for 802.3bt (POE++). Please suggest.

  • 0 in reply to SUMIT RANJAN
    TI__Mastermind 40885 points
    Hi Sumit,

    The datasheet says it is rated for 1.7A. This is just at the range for Type 4 power of the BT standard with full power, 100m of cable, and min PSE voltage at 90W.