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PoE PD controller selection

user4255914
Prodigy 20 points
Other Parts Discussed in Thread: TPS23754, TPS23756, TPS23756EVM, TPS23752, TPS23751, PMP6812

Hi Ti,

I have a case with RJ45+PoE function. The product power is above 13Watts( for LCD power is about 10W). And a auxiliary DC12V is needed for backup. The final output voltage is designd for 5V application. So for this situation, which PD controller for 802.3at Type2 is suitable now, TPS23754 or TPS23756 is right?

If DC12V is added, which stage is good for DC12V input？

Besides, how to get contact with Ti Shenzhen FAE team for PoE case?

Thanks!

 

From Jasper

20150120

  • 0
    TI__Mastermind 42795 points

    TPS23756 can support the 12V adapter from the primary side. You can refer to the TPS23756EVM (http://www.ti.com/lit/pdf/slvu329) which can support 5V/5A output from 10.5V - 57V at the primary side input.

    You can also refer to http://www.ti.com/lit/pdf/slva306 for other adapter ORing options. For example, it may work better to add the adapter at the output of the DC-DC and then regulate down to 5V.

    For type 2 PD+DC/DC controllers supporting 12V primary side adapters, TPS23751 and TPS23752 also work with wide-range supply inputs and may provide a lower cost alternative.

  • 0 in reply to Eric Wright
    Prodigy 20 points

    For TPS23754 with isolated secondary side output（12V/2A）ORing with adapter（12V/2A）,  only ORing diode is needed for PoE priority?

    For PoE priority, do i need to cut off adapter power supply if PoE is connected after adapter? or just leave the adapter there and ignore it?

    BTW, what is the role of D14(BAT54S) dual schottky diode in reference design: PMP6812?

  • 0 in reply to user4255914
    TI__Mastermind 42795 points

    Some form of an "OR"ing device (either diode or MOSFET switch) is required with any of the three adapter ORing options (see http://www.ti.com/lit/pdf/slva306).

    D14 in PMP6818 provides two functions: The lower part allows U3-cathode to follow the RC-ramp of R14/C28 at start up providing an external output slow start. Once U3-cathode gets to the regulation point then the lower part of D14 is back biased and the RC has no effect on the loop because C28 is charged up to ~Vout. The upper part of D14 provides a path to discharge C28 when the dc/dc converter is turned off. This is so that the softstart capacitor is reset quickly in case the dc/dc gets restarted soon after being turned off.