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LM20: EMI Trouble With LM20

Part Number: LM20
Other Parts Discussed in Thread: TMP20

I'm having trouble with an EMI test, radiated immunity, with an LM20.  I have a ferrite and capacitor on both the power input and temp output pins.  The un-used pins are grounded.

ferrite

capacitor

The ground connection is quite good.  The last change to the design was to significantly reduce the impedance of the ground between the LM20 circuit and the connector at the failed frequency at test.  It significantly improved the test results. Now the ground is connected with a ground plane on two layers with several vias between the two layers.  I don't think the ground is the failure mode now.

I want to know if there are any previous test issues with the LM20 and EMI.  Are there issues with exposing the top of the device with a field.  We are testing at 100V/m.  The failure frequencies are around 300MHz, 1.8GHz and around 3 GHz.

  • Hi Eric,

    We're not very familiar with this testing, as we don't sell end equipment that requires it. What I can gather is that it is mostly impacted by cabling and PCB design. Can you give more specific detail of the failure? Is it simply that there is an unacceptable variation in the LM20 output?

    At any rate, you can try using TMP20 instead. It is a drop-in replacement for LM20 that has significantly improved current drive on its output.

    Thanks,
    Ren