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TPS23753 is used in flyback converter topology. Now we have MOSFET breaks in the field. Could it be a systematical problem?

Leonardo Leone56
Prodigy 40 points
Other Parts Discussed in Thread: TPS23753

Hi all,

We are using the TPS23753 within a PoE PD device with isolated Fly-back topology. This topology and part has been in use now for quite a while. the topology is also optimized for efficiency and is based on an older reference design.

We are now focusing quality issues as we are getting parts back from the field where the MOSFET is failing. the MOSFET (T1300 in the schematic) is broken an has a low impedance. the Power cannot start any more and the TPS23753 is getting very hot, due to the short circuit.

What we know is that the part did work before and passed our tests. Even at the customer the parts were in use for several weeks until they suddenly broke. I measured some working parts and I don't see any issues so far. Nothing is getting too hot or has a critical voltage value.

Also with ESD I do not see big issues on the T1300 as there are some protection stages before the spike would hit the device. (Ferrite, protection Diodes, Input capacitances and the transformer)

My question that I want to place here is:

Does anybody see any possible issue when reviewing the schematic?

any hints on what could be wrong or not dimensioned correctly?

I attached the schematic page.PT2_Schematics_69 (1).pdf

  • 0
    TI__Expert 7570 points
    Hi Leonardo,

    Can you simulate this issue on the other board?
    There is no possible issue in this schematic, and looks like the quality issue.

    Ben
  • 0 in reply to Ben Kuo
    Prodigy 40 points

    We have more and more boards that fail. So I think it's not only a quality issue.

    In the meantime, we found out that all boards that have a defect MOSFET (T1300 on the attached schematic) also have a broken  Resistor R1315 (4R7 in a 0402 package). I checked this on several boards. this resistor is on the drive of the gate of the secondary MOSFET.

    I seems that the Resistor might break first disabling the MOSFET on the secondary site to work. And maybe finally this leads to a breakage on the primary site. I could not yet reproduce it that way, but that is what I currently think is happening.

    The R1315 is a 1/16W (0402) resistor, on TI's eval-board this resistor is specified also to be 1/16W but is 0603 package. It could be that this resistor is not well dimensioned. My next step is to measure current (especially spikes) that might eventually break this resistor.

    I happy for any other tips and help.

    Regards Leonardo