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LM3478Q-Q1: Maximum VOUT

user4806129
Prodigy 80 points
Part Number: LM3478Q-Q1
Other Parts Discussed in Thread: LM3478

I don't understand why boost controllers (with an external FET) have a maximum output voltage rating. Why is the output voltage rating not dependant on the FETs (Vds).

  • 0
    TI__Mastermind 40080 points

    LM3478 is a non-synchronous boost controller. It need an extra FET and diode at the output side. The output volatge can be high, but is limited by the FET and the diode. High voltage diode has high loss.

    what is your output voltage?

  • 0 in reply to Helen chen
    Prodigy 80 points

    Sorry if it was unclear, in this picture VOUT(MAX) is 500V. How is this maximum rating derived and why is not limited by the MOSFET and diode voltage ratings?

  • 0 in reply to user4806129
    TI__Guru 74510 points
    You are right that the Vout is limited by the FET and diode that you choose to use, but they are external components and Vout does not have a directly connection to the IC so the IC is kind of irrelevant except for the achievable duty cycle with reasonable performance. There is reference designs for 300Vout, and you can change that to 500V if you change to suitable external components.