TPS23750: Detection problem

Umberto Frangi

Part Number: TPS23750

Hi,

my customer has a problem related to detection.

The circuit replicates the schematic of fig. 40 in datasheet with the change on Ctrm=220nF, because they need to make a longer soft start, due to low load, high current.

When they connect Vdd to the PSE, detection is never done at first tentative, but requires more than one.

Is this a normal situation?

Then they found a board that did make a detection only after an hour, so with a lot of tentatives..

Do you have any suggestion to verify and improve this situation.

Thanks

Umberto

over 7 years ago

0 Thomas Amlee over 7 years ago

TI__Genius 9230 points

Hi Umberto,

Using the designators on the figure 40 diagram, which capacitor is Ctrm?

If you increased the input capacitance (C1) beyond 0.12uF, the PD would fail detection.

Thanks,
Thomas A.

0 Umberto Frangi over 7 years ago in reply to Thomas Amlee

TI__Expert 4045 points

Hi Thomas,

Ctrm is 220nF(see my text) and Cin is 0.1uF.

Thanks

Umberto

0 Thomas Amlee over 7 years ago in reply to Umberto Frangi

TI__Genius 9230 points

Hi Umberto,

Ctrm should not affect detection.

Try manually inputting 10V on the PoE input (not just Vdd-Vss) and measure the input current on the line. If it is within the acceptable current range, then the PSE should turn on. Otherwise, you may need to look into the PSE side.

The acceptable resistance range for detection is 23.75k to 26.25k ohm.

Thanks,
Tom A.

Power management

Power management forum

TPS23750: Detection problem