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DRV8350R: DRV8350R power dissipation quesiton

albert chao
Prodigy 70 points
Part Number: DRV8350R
Other Parts Discussed in Thread: DRV8350

Dear Sir

I'm checking the power dissipation of DRV8350 and I have a question about charge pump power dissipation (Pvcp)

in the datasheet equ. 45

Pvcp = Ivcp *(VM+Vdrain)

but the charge pump output power should only be Ivcp*Vvcp

why the charge pump circuit has so much losses?

thanks!

Albert

  • 0
    TI__Guru 63690 points

    Albert,

    I am looking into this and I will get back to you.

    Regards,

    -Adam

  • 0 in reply to kuohen chao
    TI__Guru 63690 points

    Kuochen,

    The reason for this equation is because the charge pump supply is both Vdrain and VM. The doubling operation of the charge pump causes increased current so that extra voltage above the main power supply can be generated.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 70 points

    Hi Adam

    the charge pump output gound level shift to  Vdrain

    so the output power should be Ivcp*(Vvcp-Vdrain) ~= Ivcp*VM

    where is the power loss Ivcp*Vdrain?

    is VCP charge pump also work as a linear regulator?

    BR Albert

  • 0 in reply to albert chao
    TI__Guru 63690 points

    Albert,

    Sorry for the delay, I am talking with design and will get back to you this week.

    Regards,

    -Adam

  • 0 in reply to albert chao
    TI__Mastermind 19720 points

    Hi Albert,

    The Charge pump is a doubler architecture but the charge pump does not double the input voltage but just adds 12V onto the input voltage. This means that the charge pump is inherently inefficient. If you use P=IV equations to work out the efficiency of the charge pump you see that the Pout= Vcp*Icp where Vcp=(Vdrain+12V) so Pout = (Vdrain+12V)*Icp the input power is Pin= Vdrain*Icp+Vm*Icp or Pin =(Vdrain+Vm)*Icp so the efficiency is = Pout/Pin = ((Vdrain+12V)*Icp)/((Vdrain+Vm)*Icp) or Pout/Pin = (Vdrain+12V)/(Vdrain+Vm). so the charge pump is ideally 100% when the two input voltages equals the output voltage. Vdrain+Vm = Vdrain+12V.

    Regards,

    Michael