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CSD87381P: Turn on/off time and Rise/fall time

Yuto Sakai
Mastermind 6100 points
Part Number: CSD87381P
Other Parts Discussed in Thread: TINA-TI,

Hi,

Could you tell me if there is information of maximum of the following parameters?
What percentage of Typ value is it?
It is not necessary to be a guaranteed value.

・Turn ON Delay Time(Tdon)
・Rise time(Tr)
・Turn OFF Delay Time(Tdoff)
・fall time(Tf)

Best regards,
Yuto Sakai

  • 0
    TI__Expert 6795 points
    Sakai san,

    Thank you for asking and considering TI MOSFETs.

    We do not put maximum values into the switching times, using these values as a guarantee of switching performance may have little indication as to how the device performs in circuit.
    The values in the datasheet are highly dependent upon drive strength, board layout, circuit schematic and conditions. As such these values are a good relative indication of faster or slower when comparing TI mosfets (this is not even a good specification to compare between MOSFET manufacturers as they all have different circuits or conditions) but not for absolute performance.
    A better indication of switching speec would be to look at the RC time contant, Rg*Ciss or Rg*Qg where typical and max is given.
    We also have written a blog here for some more information: e2e.ti.com/.../understanding-mosfet-data-sheets-part-5-switching-parameters
  • 0 in reply to Chris Bull
    Guru 11170 points

    Hello Chris,
     
     What is the theoretical tolerance of these values? No guaranteed　value OK.
     
    Regards,
    ACGUY

  • 0 in reply to ACGUY
    TI__Expert 6795 points
    Nagai san,

    This is not something we have ever looked into for these parameters as they are a pretty useless part of the datasheet as every application , layout, drive scheme changes the switching speed of a MOSFET.
    As referenced previously the better way to determine switching speed would be to use the RC time constant, you can use the datasheet parameters for these to look at theoretical maximum, the likelyhood of having a device with both max charge/capacitance and max Rg is very low but in theory this is possible.
  • 0 in reply to Chris Bull
    Guru 11170 points
    Hello Chris-san,

    Thank you for reply.
    I sent my opinion to customer"if you want to know switching delay time for FET, please refer to the parameters(Vgth, Rg, Qg, Cxss) and calculate " .
    However, they are requesting a TI's point of view. That is because they are asked by the end customer to explain the designed worst condition.
    I tried download and import the PSPICE model to TINA-TI, but import failed.
    I tried calcrate about maximum tpd from datasheet listed parameters that result was about 22-nsec. I can't judge this result as correct.

    We need your help. Please.

    REgards,
    Nagai.
  • 0 in reply to ACGUY
    TI__Expert 6795 points
    Nagai san,

    The Rg in the CSD87381P spec for the low side device has a typical of 1.25Ohm and max of 2.5Ohm. So a 2x or 100% potential variance.
    The Ciss and Qg both have a variance of ~30% from typical to max. So this means from typical a device could vary in time constant up to 130% over typical.
    This is how much the switching time could be impacted given a worst case device based on the datasheet. This is highly unlikely but is what the datasheet suggests.
    We do not test for min so I can not give you a number on the low side, I would also use a similar number for typ to min, this would be safe.
    Again a reminder, the datasheet switching time has absolutely nothing to do with how the part will switch in application and as such this calculation is in no way close to how a part actually performs in circuit as the customer will have a totally different drive circuit and layout vs the test circuit for the CSD87381P.
  • 0 in reply to Chris Bull
    Guru 11170 points
    Thank you for your commnts.