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TPS40195 resistor parallel or serial to CBoost

Andreas Kirchgraber
Intellectual 370 points
Other Parts Discussed in Thread: TPS40195

Hi,

where is the right position for R4?

In Tina TI an The User Guide for the TPS40195EVM R4 is parallel to CBoost:

In datasheet R4 is serial to CBoost:

 

What's right?

 

regards

Andreas

  • 0
    TI__Mastermind 25296 points

    the right connection, regarless the controller, is to have 

    BOOT / C12 / R4 / SW

    connected in serie...

    the reason is that the R4 helps reducing the switching current (acts like a gate resistor in both turn on / off processes of the high-side power FET)...

    in brief, it work like a resistor between pin 16 and HS_gate...

    V.

  • 0 in reply to Vincenzo Pizzolante
    Intellectual 370 points

    ok, then it seems SwitcherPro is also wrong:

    Will this be corrected in a newer version?

    Also R4 is stated in B.O.M. of SwitcherPro as 2W resistor with 2512 package.

    In the EVM R4 is a 63mW with 0402 package.

    Which package will be sufficient?

    regards

    Andreas

  • 0 in reply to Andreas Kirchgraber
    TI__Mastermind 25296 points

    no way, 2W for such resistor  :(

    as gate resistor it is enough a 0603 or even 0402 SMD package, in according to EVM, as it should be...

    normally it depends on the driver current peak capability, in combination with the FET selection, since the peak current of 0603 is a bit higher than the 0402 package...

    for example if you have a single HS FET with a not "huge" Qg then 0402 is enough, but if you starts to have many in parallel (so the total Qg quickly increases) the driver should provide a very high peak current (this depends on driver)... if this peak is higher than 1Amp, the 0402 package is NOT reccomanded...

    so, if you don't need extreme integration, just use the 0603...

    V.

  • 0 in reply to Vincenzo Pizzolante
    Prodigy 110 points

    Dear Sir,

    I am a college of the the previous requester akircan and I  would like to know which schematic is correct.

    In the moment akircan and I assume  that the connections of R4 and C12 to TPS40195 and to all  MOS-FET

    in the following schematic part from the TPS49195EVM User Guide  is correct

    Do you agree?

    Best regards

    Reiner B.