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Part Number: DRV8350R
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?
I am looking into this and I will get back to you.
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In reply to Adam Sidelsky:
In reply to kuohen chao:
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.
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?
In reply to albert chao:
Sorry for the delay, I am talking with design and will get back to you this week.
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.
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