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TPS54325/about SW waveform

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: TPS54325

Hi,

Could you tell me about TPS54325 SW waveform?
Can you check the attached file?
TPS54325.pdf
SW wave form slew rate is different in light load and heavy load conditions.
Why is that?
Could you give me your advice.

Best Regards,
Yusuke/Japan Disty

  • 0
    Guru 21930 points

    Hi,

    Can I get the information?

    If you need more information or if  I should  clarify my comment ,

    please let me know.

    I’m so sorry to rush you but please support this.

    Best regards,

    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 191445 points
    It is different because of the dead time. It higher loads, the low side body diode clamps the SW node at minus one diode drop below GND. If the current is negative, that diode does not conduct. the current must charge the parasitic capacitance of the FEts so the voltage can rise to one diode drop above VIN so the high side body diode can conduct. Remember the inductor current must remain continuous.
  • 0 in reply to JohnTucker
    Guru 21930 points

    John-san,

    Thank you for your support.
    I can not understand the relationship between the dead time and slew rate.
    Could you tell me about this issue more detail?

    Also,When a light load and a heavy load,
    Is this device changing the dead time?

    Best regards,

    Yusuke/Japan Disty




  • 0 in reply to Tsukui Yusuke
    TI__Intellectual 2590 points
    Hi Yusuke-SAN,

    TPS54325 has dead time before both high side and low side MOSFET on. When low side is turn off, there has about 20ns dead time, both high side and low side is off. If the loading is 0A, the inductor current is reverse current, so the current will go througn high side's bidy diode and charge Vin up. so the waveform's SW rising rew rate generate by reverse current of indcutor, that's why slew rate is less than heavy load.
    thanks!