> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of res0qrqr@verizon.net
> Sent: Saturday, September 24, 2005 12:18 PM
> To: Microcontroller discussion list - Public.
> Subject: [EE] 74-series logic power consumption
> 
> 
> Well, I know this has been covered before, but a stroll 
> through the archive didn't seem to find a direct answer.  
> So here goes once again:
> 
> I'm building a circuit using 74HC discrete logic (and a 
> 16F872, to keep this on topic) and have become ever more 
> confused by all the 74xx families that seem to exist.  In 
> my particular circuit, a 74HC132 demands 275 microamps of 
> 5-volt power when handling a 1 MHz signal.  But at 50 MHz 
> (Yikes!) the power consumption goes up to a whopping 12.9 
> milliamps.  Too much.  Batteries too dead, too soon.

Supprised HC is working for you at 50MHz clock rates, the prop delay
through the average HC gate is nearly 1/2 your clock period at 50MHz.

All CMOS parts consume more power the faster you clock them.  They also
consume more power depending on the load they must drive.  Reduce the
load capacitance and the power will go down somewhat.

In general, VHC has a lower dynamic power consumption than HC.  Can't
say if it is 1/2 or 1/3 or 1/8 but I do remember that it is lower.

Any of the Bipolar families (S, AS, LS, ALS, F, etc) will consume much
more power than the CMOS families.

If you can run your system at 3.3V then you can consider some of the
other low-power CMOS logic families like LVX and LCX or LVT and LVTH.
However LVT and LVTH are built with a BiCMOS process and might consume
more power than the fully CMOS parts. 

Fairchild Semi (www.fairchildsemi.com) has some application notes that
show general power consumption vs clock speed for various logic
families.  TI and National and ON-Semi probably have similar
information.

Rob 
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