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J/K Selection Method for TPS40170

Anthony Boulard
Prodigy 110 points
Other Parts Discussed in Thread: TPS40170

Hi !

I'm trying to design a buck converter using the TPS40170 ans the J/K method described on the datasheet (page 33)

I've already looked at the post named " J/K Selection Method for MOSFET Selection " but I'm not able to applicate the method with values given in the datasheet of the TPS40170.

For the High Side MOSFET :

Values I use :

Vin = 24V

Idrive = (Vgate - Vth)/(Rdrive + Rgate)

with Vgate = 8V, Vth = ? (MOSFET not already choosen...), Rdrive = 2,64 ohms, Rgate = ? (MOSFET not already choosen...)

Qg/ Qsw = 2

Vdrive = 12V

Fsw = 300kHz

Vout = 5V

Ipp = ? 

 

If you can help me to find Ipp, Vth and Rgate values (or the method to find them) ...

Thanks You !

Anthony

  • 0
    TI__Mastermind 35115 points

    Hi Anthony,

    The Ipp value is the inductor peak to peak current ripple. This can be found using Equation 19 but replacing "0.3 x Iout" in the denominator with "Ipp" then solving for Ipp.

    For Vth and Rgate I suggest starting out with the values near the ones for the MOSFETs on the EVM. This would be Vth = 3.0 V and Rgate = 1 Ohm. Once you start narrowing your MOSFET selection you can replace these with real values then check if there is any change in the result.

    Hope this helps.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 110 points

    Hi Anthony,

    Thanks for these precision !

    Regards,

    Anthony