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TPS23730: TPS23730

kiran surve
Prodigy 170 points
Part Number: TPS23730

Hi,

We have designed Isolated Class 6 POE++ power supply as per reference schematics PMP22494_RevA_SH2.SchDoc using TPS23730 IC.

In no load condition we have maintain output load by adding bleeder resistor on 12V, such that input current on POE RJ45 input is >18mA with input voltage from 44V to 52V

During circuit operation the input wattage on RJ45 PD input is dynamic and ranges from 6W to 25W in one case and 6W to 45W in another case.

We had put Classification resistors CLSA = 31.7 ohms (27 ohms + 4.7ohms) & CLSB = 130 ohms (120ohms + 10 Ohms).

DEN pin is connected with 25.5K resistor to VDD as in the reference schematics.

The PSE output would be from Type 2 802.3at or Type 3 802.3bt Ethernet swtich.

What should be the condition of EMPS pin, should we enable or keep disable by connecting to PGND?

What is the significance of EMPS pin?

The circuit would operate as usual with PSE input by performing class identification.

Regards,

KIRAN SURVE

  • 0
    TI__Mastermind 37071 points

    Hi KIRAN,

    Thanks for reaching out. 

    In you description you added a bleeder resistor on load to maintain >18 mA MPS current. And TPS23730 has the EMPS can do it automatically so you do not need to have the bleeder resistor as a dummy load. You can leave this EMPS pin open to enable the auto MPS.

    The MPS pulse width depends on the negotiation it made. If it is made with a AT Type-2 PSE, TPS23730 will automatically adjust the MPS duty cycle to 26.6%; if it is a BT Type-3 PSE, it will be 3%. Both cases will meet the MPS requirement to make sure the PSE won't turn off the port due to loss MPS.

    Best regards,

    Diang