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TMS320F28379D: VDDA_3V3 Damaged

Nitesh Malik
Prodigy 50 points

Part Number: TMS320F28379D

Hi Forum,

 

I am using TMS320F28379D in a Railway project where i am using it to control PWMs for IGBTs. During testing when ever there is any blast of IGBTs happening the VDDA_3V3 power rail is getting damaged. This has happened in 5 controllers. What can be the issue of this, or is there some protection iam missing.

On ADC input i have a clamping diode of 3.6V.

Please suggest what protection or changes i can do in design to avoid this.

 

Regards,

Nitesh Malik

  • 0
    TI__Expert 8980 points

    Hi Nitesh,

    Are analog pins or VDDA seeing a transient higher than the expected clamp level? Even though you have a 3.6 V clamp on the ADC input, the transient may still couple via the board (via ground bounce, via shared analog-/digital-ground, via power rails) to the VDDA line. Also, are the blasts causing negative transients or undershoots? If the diode only clamps positive spikes, negative spikes may still damage internal analog circuits.

    Second, a series resistor between the signal source and the clamp/ADC pin can help limit injection current and decouple fast spikes, you might need RC or LC filtering on the analog input to suppress high-frequency transients.

    On high-power switching boards layout is critical: the return currents are large and rapid, stray inductances exist; if your MCU ground returns are shared with heavy switching currents or if the analog ground path is not isolated, you will see the “blast” noise show up on VDDA or the ADC domain.

    Finally, use a low-impedance LDO for 3.3 V analog supply, decoupled closely to the MCU. Add a ferrite or small series inductor in the VDDA feed, plus decoupling caps (100 nF + 1 µF near the pin).

    Best Regards,

    Masoud