Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!samsung!rex!wuarchive!sdd.hp.com!hp-pcd!hpsgwp!plim From: plim@hpsgwp.sgp.hp.com (Peter Lim) Newsgroups: sci.electronics Subject: Re: 80386. Message-ID: <4400001@hpsgwp.sgp.hp.com> Date: 14 Jan 91 08:36:43 GMT References: <1990Dec18.234020.2491@uoft02.utoledo.edu> Organization: HP Singapore IC Design Ctr Lines: 32 / dana@locus.com (Dana H. Myers) / 2:14 pm Jan 10, 1991 / $ The 25Mhz chips DO run hotter than the the 16Mhz parts. CMOS power $ consumption occurs during transitions. There are two reasons why;(1) $ current must flow through the gate capacitances (standard 1/(2*pi*f*C) $ stuff) and (2) there is a brief instant when both the P and N channel $ FETs are conducting. Resultantly, the power consumption of CMOS parts $ is roughly proportional to frequency of operation. A 25Mhz will consume $ about 25/16 (or 150%) of the power a 16Mhz part consumes. $ If I remember correctly, the energy dissipated in a CMOS chip is proportional to the square of the frequency. So, 25 MHz vs. 16 MHz power supply would be 25^2 / 16^2 = 244 %. Quite a hell lot more power. Assuming voltage and impedance stay about constant, heating rate of the chip will be about proportional to power dissipation. But since higher temperature will give rise to higher rate of heat loss; may be a part running at 25 MHz will be about twice as hot as a part running at 16 MHz. (Somehow, can't quite remember the equation that says that power is proportional to freq^2). Regards, . .. ... .- -> -->## Life is fast enough as it is ........ Peter Lim. ## .... DON'T PUSH IT !! >>>-------, ########################################### : E-mail: plim@hpsgwg.HP.COM Snail-mail: Hewlett Packard Singapore, : Tel: (065)-279-2289 (ICDS, ICS) | Telnet: 520-2289 1150 Depot Road, __\@/__ Singapore 0410. SPLAT ! #include