TPS23750: Schematic Review Request

Hello Nicky,

1. Are you doing detection with a large (low impedance) load?

2. If not #1, then check the 4th paragraph of page 16 of the TPS23750 datasheet: www.ti.com/.../tps23750.pdf
Your diode bridge may have some leakage current that, so using a smaller resistance may be helpful.

Best,
Thomas A.

Hi Thomas,

1. No Load. Only scoping.

2. Using HD06. Only described below spec.
Average Forward Rectified Current
Peak Reverse Current at Rated

Regards,
Nicky

Nicky,

1. In what way is the device not working properly? Not outputting power? Is detection/classification occurring?
2. What is your output power?

Thanks,
Thomas A.

Hi Thomas,

Set output voltage to 5V.

But its output is as attached. (Measured on J2 in schematic)

Regards,

Nicky

Nicky,

Sorry for the late reply. Your schematic looks good. Same components as the EVM. Let me get some additional eyes on this, then I can work to find a resolution.

Do you have the BOM for this design?

- Thomas A.

Hi Thomas,

Customer has some questions as below

1. There are 2 kinds of EVM. One is buck, the other is flyback.

    Could you let me know the difference between 2 EVM and which one is more stable?

    And the difference between isolated design and non-isolated design.

2. There are about 500mV ripple without load. (see Attached).

    Is this ripple is normal? Could you let me know normal ripple level of PoE PD without load?

3.  If customer wants to use Gb ethernet, does she need to change the circuit?

    If yes, how she can make it?

Regards,

Nicky

Hi Thomas,

Please let me get your answer ASAP.

And customer designed Flyback type circuit as attached.

Please review this schematic and let get the result also.

Regards,

Nicky

POE171012Flyback.pdf

Hi Nicky,

To answer your questions:

1. A non-isolated buck design would have a shared ground plane between the RTN plane & the converter outuput (-Vout rail). An inductor is used to store energy for the power conversion.

An isolated flyback design works the same way as a buck converter, but instead of an inductor, a transformer is used to store energy. Transformers provide isolation between the RTN plane and the -Vout rail by transferring energy between 2 inductors, magnetically.

For more information about the differences between these two topologies, I recommend TI's "World of Power" Series: training.ti.com/world-power

The main difference between the two topologies is that the isolation of the ground planes prevents conducted emissions from the noisy power converter from traveling to the ethernet input where it may interfere with data signals. For design recommendations on isolated design, I recommend this app note: www.ti.com/.../slua469.pdf

Buck converters are generally used at type 1 power applications because the noise generated from the converter is smaller in magnitude.

2. I will take a measurement of the EVM and let you know.

3. To use gigabit ethernet, she will just need properly terminate the data side of the ethernet transformer and connect it to a gigabit PHY. This power level should not interfere with the designers ability to get gigabit speeds.

Thanks,

Tom

Nicky,

On the schematic, be sure that the TVS diode, D3 is between VDD & VSS, not RTN.

Also, as a double check, make sure the BOM changes are in line with the desired output: pg 6 of www.ti.com/.../slvu137d.pdf