The pd chip TPS23754PWP used by the customer was tested by pda600 and failed by Rdet_Voffset. Please help to analyze the impact scope and cause of the problem
Hi Xiaofu,
Rdet_Voffset is the approximate full wave bridge DC voltage offset.
I am not an expert of pda600, while I would suspect the detection measurement circuit is like the diagram below.
The nominal detection voltage of pda600 is 4 - 8 V, if it shows ~2.5 V estimated voltage drop on the diode bridge, that means about 1.5 - 5.5 V voltage on the detection resistance.
While, DI208S looks like not a Schottky diode based bridge, and its forward bias is around ~0.75 V at low current. So you may have ~1.5 V voltage drop from the diode rectifier. The rest of voltage drop may come from inductors or ports which showed some nonlinear behavior and was considered as diode bridge voltage drop. You may try to use a Schottky diode based bridge to see if Rdet_Voffset gets reduced.
Could you send me the datasheet of 56A-S1188L1-E211? By the way, it makes more sense to me if the common-mode chokes are placed on the data side rather than the power&data mixed side. Since the PoE pairs has a common-mode current which could saturate the chokes.
Best regards,
Diang
Hi Xiaofu,
Thanks for the documents.
The symbols may be different in the datasheet and your schematic but seems the CM choke is at the data side.
Could you try the following things to see if it got improved?
1. Short FB38 & FB39 to by pass them.
2. Try with Schottky diodes at D1 & D6 which have lower forward voltage drop.
3. Try to desolder R1 & R2 which could be considered as loads and make voltage drop.
4. Try to desloder the Bob Smith Termination as there is no 2-kV capacitor in your case.
I will close this thread for now as we have not received your reply for a relative long period. Please try the steps above and open new thread if you have any further questions.
Best regards,
Diang
