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From: scott@hpcvca.CV.HP.COM (Scott Linn)
Newsgroups: sci.electronics
Subject: Re: 80386.
Message-ID: <3340012@hpcvca.CV.HP.COM>
Date: 15 Jan 91 18:44:24 GMT
References: <1990Dec28.210731.10685@zoo.toronto.edu>
Organization: Hewlett-Packard Co., Corvallis, Oregon
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/ hpcvca:sci.electronics / dana@locus.com (Dana H. Myers) / 12:51 pm  Jan 14, 1991 /

>Power is given by:
>
>	P=IV		
>
>    Where:
>	P = power in Watts
>	I = current in Amperes
>	V = voltage in Volts

Right, and I = C * dv/dt, so P = C * V * dv/dt.

In CMOS dv is equal to the supply (transitions are from supply to
ground), so P = C * V^2 / dt.  But, 1/dt is the same as switching frequency,
so Pdynamic = C * V^2 * f, not

>	Pdynamic = V^2 * 2 * Pi * f * C,

which gives you a value over 6 times larger than the actual power
dissipation.

Scott Linn