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LM5576: Radiated EMI performance, Layout issues?

Bart
Expert 6460 points
Part Number: LM5576

Hi team,

we are using 2x LM5576MH as a step down from 15V-60V to 4.4V, the output current is max. 2A. The two units are powering LED matrix working in a multiplex configuration (around 1kHz). 

We have two issues:

a) Radiated EMI - we observe 2-3V peak of a width of around tenish nanoseconds -> This generates harmonics and increases EMI. At the moment we would need to lower the EMI by 5-10dB (we have -3dB now).

b) We have hade a few instances (3-4 from hundreds of units) of the device getting burnt when the main power supply was turned on (also damaging the tantalum cap. 6.3V).

Can you advise what can be done to resolve both points?

The PCB is 4x35um. I have attached some schematics.

Thanks for your help.

  • 0
    TI__Mastermind 39980 points
    Hello Bartosz,

    would you mind emailing me at David.baba@ti.com so I can review your layout files on Altium?

    In general I advise the following.

    1. Use a shielded inductor
    2. keep the Switch node minimal in size.
    3. Make sure the Cin ceramic is close to Vin and Gnd of the Device.
    4. Make sure the Connection between Switch and inductor is short
    5. Make sure the connection Between Switch and Anodoe of diode is short.

    Regarding the device failing have you ensure the input filter is well damped? if so, it may be related to the layout also. i can give you specific instruction if you email me the files. See link below on damping input filter. suggest parallel damping approach detailed therein.

    www.ti.com/.../snva538.pdf

    Hope this helps?

    David.
  • 0
    TI__Guru 73072 points

    Hi Bartosz,
     
     This article may be of interest:
    www.how2power.com/pdf_view.php

    Regards,
    Tim