Dynamic power question

[deepa187]

Hi,

I want to estimate the dynamic power with given voltage and frequency. I know the formula for that is cV^2f.

If V is given 4 volts and f is given 800 MHZ. How do I calculate the dynamic power (estimation) in watts?

Regards,
deep

 

[Idontcare]

Welcome to the forums deepa187!

See this thread here for some discussion on that topic 😉

If you are solely interested in the dynamic power, ignoring the temperature-dependent static-power, then you need a way of estimating the capacitance of the IC in question (the variable "c" in your posted equation)...and be aware that capacitance is application dependent 😉 😱 as it depends on the specific suite of instructions being called upon during the calculations.

If your processor happens to be a quad-core sandy-bridge or quad-core ivy-bridge then the effective capacitance happens to be known (for the application is Intel's BurnTest) then you are in luck as I have experimentally arrived at the following capacitance for those two specific processors:

(answer: approximately "15" for both)

 

[TuxDave]

At 15nF for dynamic capacitance, 4V @ 800MHz = The maximum power delivered by your power supply before fuses blow since the Ivybridge transistors would probably short out.

 

[deepa187]

Hi,

Many Thanks for quick response.

P(dynamic) = c* 4*4(volts)*0.8(GHZ)

What is unit of capacitance here? is it nF?

if it is, so I will give me results in watts? Please correct me if I am wrong.

Regards,
Deepa

 

[TuxDave]

Hi,

Many Thanks for quick response.

P(dynamic) = c* 4*4(volts)*0.8(GHZ)

What is unit of capacitance here? is it nF?

if it is, so I will give me results in watts? Please correct me if I am wrong.

Regards,
Deepa

Yes, nano to balance the giga in the clock frequency.

 

[Abwx]

Should multiply the terms above by the pulsation 2pi.

Formulae is Pd(V,F,C) = V^2/(1/2pi.FC) = (V^2).(2pi.FC)

F in GHz and C in nanofarads for ease of calculation as pointed by Tuxdave.