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TPS54308EVM-876: TPS54308EVM-876

Zhanpeng Li
Intellectual 2140 points
Part Number: TPS54308EVM-876
Other Parts Discussed in Thread: TPS54308

Hi,

During testing  the voltage between SW to GND, i found these had ringing at switch-node and cause a spike voltage. i hope to know how to reduce this ringing and spike voltage.

  • 0
    TI__Genius 10070 points

    Hi,

    1. Let the test loop short to reduce the noise

    2. Add snubber circuit

    3. change boot resistor to 10ohm or 20ohm

    Shawn

  • 0
    TI__Intellectual 2140 points

    Dear all,

    Since i already solve this problem for my customer. I summarized the cause issue and solution as follow:

    Cause issue:

    1: PCB Layout do not have good performance on paraitic inductance reduce. You may can find the following adress to know much about it.

    http://www.ti.com/lit/an/slyt682/slyt682.pdf

    2:the switching speed is too fast may cause this ringing too. dv/dt should be controlled in a reasonable range;

    Solution:

    1: Add Ron between Gate drivers to MOSFET can help reduce dv/dt;

    this solution may not suitable for our TPS54308 because TPS54308 integrated MOSFET and Gate drivers inside;

    2:Add 3.3ohm boot resistor in Bootstrap circuit

    We can change our circuit as follow:

     

    Here we have the result on this solution:

    Ringing can be reduce and spike voltage is 25.2V due to boot resistors;
    3:Add RC snubber circuit on SW to GND;
    when switch turned off, while the energy stored in the parasitic inductance charges the parasitic capacitor of the switch, the absorption capacitor is charged through the absorption resistor.Due to the effect of absorption resistance, the impedance becomes larger;
    When the switch is switched on, the absorption capacitor discharges through the switch, and its discharge current is limited by the absorption resistance.
    It's very important to choose a suitable parameter of C/R. However, it's difficult for us to calculate exact value. Though our TI power design tools, we can simplified calculation process.
    The tools we used call  Power stage designer. We can download this tools in TI.COM- Design resources- Power stage designer.
    you can find every detail in this tools