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TPS23731: Multiple retries before POE go normal operation

Poh Kok Keng
Genius 5512 points
Part Number: TPS23731


hi expert, 

I have question about TPS23731

a. with PoE switch TL-SG1005P V2 that mounted with TPS23731, i noticed multiple retries before the POE enter normal operation. Is this normal? and if Yes, how to avoid this? 
PoE block- start up
a. i also tested with PoE switch TSW100000000 (Teltonika) -> Look good! without multiple retries. 
PoE block - startup
Q2: Regarding Earthing screw on PoE switches.
- Do we need to earth PoE switches?
- Do we need the earth at our end (device)?
Best Regards,
Felix
  • 0
    TI__Mastermind 37121 points

    Hi Felix,

    Looks like both PSE are at/af standard compliant. Could you share your PD schematic? We want to check the classification resistance you set.

    Earthing ground depends on the end product standards normally. Usually VSS or RTN won't be connected to earth ground.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Genius 5512 points

    hi Diang,

    1. Classification resistor R1223=63.4ohm 1%.
    2. Regarding Earthing screw on PoE switches.
    Earthing ground depends on the end product standards normally. Usually VSS or RTN won't be connected to earth ground.
    Designer is asking will that cause earthing issue? Or you had recommended your customer to earth their product?
     
    Why do PoE switches have those provisions for earthing screws....
    Best regards,
    Felix
  • 0 in reply to Poh Kok Keng
    TI__Mastermind 37121 points

    Hi Felix,

    Thanks for your reply. 

    1. The classification resistance looks correct. It may be a problem about PSE. For example, if PSE in semi auto mode, it is is possible to have multiple cycles. You may need to check with the PSE owner. 

    2. The ground on the output side depends on the end equipment applications.  It could be connected earth, chassis, floating... But normally the VSS and RTN on the PD side is not connected to earth. Below is an example of earthed PD application which you can find in www.ti.com/.../slua736.pdf

    Best regards,

    Diang