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TPS7A4001: EMC PROBLEMS

paolo malagoli
Prodigy 20 points
Part Number: TPS7A4001
Other Parts Discussed in Thread: TPS7A4101,

Hello,

we're experiencing EMC problems on the TPS7A4001DGN.

The issue happens when a cellphone is placed close to the component (close means closer than 10 inches).

The output then starts switching off and on, for an unpredictable time ranging from few milliseconds to hundreds of milliseconds.

This of course causes problems to the devices connected to the regulated power supply.

During our tests we have tried to replace, in the same circuit, the TPS7A4001 with other linear regulators. mong them, we have seen that using the TPS7A4101 we can't see the issue.

The TPS7A4101 should be the 50V version of the TPS7A4001.

Is there any known reason for which we see this difference?

Thanks

Regards,

Paolo Malagoli

  • 0
    TI__Guru 55940 points
    Hi Paolo,

    Do you have any scope shots of Vin, Vout, and Iout that you could provide? It would also be helpful if you could provide the schematic around the LDO (Cin, Cout, feedback resistors, etc).

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 20 points

    Hi Ryan,

    our Vin ranges from 7 to 32V depending on application. We're able to stand overvoltages up to 80V.

    The application schematic is this one below:

    I have to say that I made a mistake in the p/n we used without having problems: it is the TPS79850, so a different LDO,not the TPS7A4101.

    The main difference in my opinion is therefore the fact that the affected part is an adjustable and the non-affected is fixed output.

    My question now must be changed in: are you aware of any possible EMC issue which can be caused by the internal FB circuit of the component?

    Thanks

    Best Regards

    Paolo

  • 0 in reply to paolo malagoli
    TI__Guru 55940 points
    Hi Paolo,

    There are actually two factors that can potentially make TPS7A40 more susceptible to EMC than TPS798. You identified one already, the FB node is more exposed for TPS7A40 as it is outside the device; however, there is no dedicated shielding of the FB node on either device. The more likely reason that TPS798 is less affected by your EMC test is that TPS798 has higher ground current. You could test this by trying TPS79801 which is also an adjustable device.

    Very Respectfully,
    Ryan