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TPS23756 EVM. High temperature loss...

G.S.Lee
Intellectual 465 points
Other Parts Discussed in Thread: TPS23756, TPS23753A, TPS23753AEVM-001, ISO721, TPS28225

Hi all,

I'm testing PoE with TPS23756 EVM and SLVU329A.pdf .

1. In schematic , R3 (10 ohm) and D7(zener) are representing high temperature loss.

  Can I increase R3 to reduce loss ?

2. I need PoE circuit   8V / 500mA  (4.5W) with Low temperature generation.

   Our main circuit  is weak to high temperature.

   How can I achive it ?

Best regards,

Lan jackey.

  • 0
    TI__Mastermind 40100 points

    Hi Lan,

    1.  R3 is expected to get hot at higher input voltages. You might be able to get away with a higher rated resistor or a more optimized heat dissipating resistor. Otherwise you can reduce the capacitor C11 to reduce the power to the resistor; however, be sure that you measure the gate voltage of the synch FETs because changing the value will affect the gate drive on the secondary at low input voltage (12V).

    This will be an interative process on the EVM to get the sweet spot for your application but should be the best start.

    2. 8V is not a common output voltage. I was able to find PMP6584 but it maybe overkill for your application. So I recommend designing the PD with the TPS23753A for lower power designs and using SLVA305C application note to design a simple flyback converter. If you'd like to see what other poe options are available, please look at our Poe reference design selector in the right side of the ti poe website.

    http://www.ti.com/ww/en/analog/poe/index.htm?DCMP=hpa_pmp_general&HQS=Other+OT+poe

  • 0 in reply to Darwin Fernandez
    Intellectual 465 points

    Dear Fernandez,

    I think the PMP6584 is most efficiency circuit. It doesn't have any high temperature parts.

    Thus, my plan is following. Check it  whether it is correct or not, please.

    1. TPS23753AEVM-001 circuit should be based. 

    2. Low efficiency circuits of it should be changed with following parts in PMP6584 circuit.

       - T4(50:1 transformer) , TPS28225, SIR838, TPS71550, ISO721 :

    3. TPS23753EVM has output 5V. Thus R15, R17 will be tuned for 8V output.

    Does my plan is correct?

    Best regards,

    Lan

         

  • 0 in reply to G.S.Lee
    TI__Mastermind 40100 points

    Hi Lan,

    1) Yes, you can probably modify this EVM for your testing.

    2) The TPS23753A EVM and PMP6584 are different topologies. Since SLVA305C is a design for Flyback with diode rectifier, you can modify the EVM (flyback with diode rectifier) to see what specific components you need.

    3) You can change R15 and R17. But you should verify stability first. Then you can tweak the compensation as necessary using SLVA305C. Be sure to fully test your solution. Modifications to components can be done using SLVA305C as a design reference.