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TPS53355 / Current slew rate of High side switch

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: TPS53355

Hello,

Could you please let me know the current slew rate of High side Switch which is integrated in TPS53355?
Please see the attached image as High side switch current slew rate.
I understood that current slew rate is decided by FET specification, parasitic of PCB and peripheral patrs.
However, please let me know an approach of getting high side switch current slew rate.

Our customer would like to know this parameter for improving the EMI noise by High side switch.
I already inform the BOOT register

Best Regards,
Ryuji Asaka

  • 0
    TI__Guru**** 191445 points

    I think you may be asking the wrong question.  The current waveform in the high side fed at turn on is a little complicated and I don't think there is any practical way to measure it.  When the low side FET turns off, the inductor current must remain continuous.  The current flows thru the low side body diode and the switching node is clamped one diode drop below ground during the dead time.  When the high side is turned on and the gate drive gets above the threshold, the drain to source voltage is still VIN + 0.7V.  In this condition, only the internal parasitic inductance is limiting current as the low side body diode is in reverse recovery.  The currents can get quite high for a couple nsec.  After the reverse recovery, the high side drain to source is Vin - Iout*RDSon and the internal switch current goes down to the inductor current level.  To further reduce EMI, you may want to pay close attention to layout and possibly add an RC snubber and additional high frequency filtering.