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Original question:

Isolated DC/DC converter or non isolated DC/DC converter for PoE application?

TPS23730: PoE When is the isolation required / Buck converter

d_zero
Genius 4885 points
Part Number: TPS23730


Dear All,

i have one question regarding IEEE 802.3bt isolation requirement. It is not clear from the 33.4.1 chapter.

We have a camera that only has one connector industrial ethernet connector and it is in metal housing

1) Shield of cable is connected to shield of connector and it is connected to device Housing -> Housing is earthed.

Do we need isolation on PoE  power? Can we use BUCK instead of FLYBACK?

2) So inside the device the PCB GND is floating

2a) is it ok to connect ESD diodes on MDI lines ( between eth phy and magnetics) to PCB GND? or do we need to put ESD diodes on the other side of eth magnetics and connect to Shield?

2b) is it ok for EMI purpose to connect PCB GND to device HOUSING via 2kV CAP and parallel resistor near the ethernet connector?

3) How can we use TPS23730 in BUCK configuration?

Best Regards,

David.

  • 0
    TI__Mastermind 21320 points

    Hey David, 

    Isolation for the DCDC is not required of PoE. It depends on the application. The same is true for being connected to Earth ground or left floating. Different end equipment have different requirements. A nurse calling station in Chicago has different requirements than factory lights in China. 

    The following paper is a good reference for what we recommend for surge protection in earthed and unearthed applications: 

     

    But you will notice that nonisolated designs are not included. Nonisolated designs do not afford the best surge protections like isolation does. 

    The TPS23730 is a PoE-PD + a PWM controller, so please see the following reference design that uses the same type of IC in a buck:  

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

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments