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

over 4 years ago

0 Adam Sidelsky over 4 years ago

TI__Guru 61190 points

Albert,

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

Regards,

-Adam

0 kuohen chao over 4 years ago in reply to Adam Sidelsky

Prodigy 10 points

Any result?

0 Adam Sidelsky over 4 years ago in reply to kuohen chao

TI__Guru 61190 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 albert chao over 4 years ago 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 Adam Sidelsky over 4 years ago in reply to albert chao

TI__Guru 61190 points

Albert,

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

Regards,

-Adam

0 Michael.Walker over 4 years ago 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

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DRV8350R: DRV8350R power dissipation quesiton