On Thu, 14 Aug 2008 15:11:04 -0700, Chops\ wrote:
>
> On Jul 31, 2008, at 4:36 PM, Vitaliy wrote:
>
>> Cost is really the only important factor for this application (driving
>> an LED).
>>
>
> I've been wondering about using "tiny logic" for LED driving.  Price on
> something like a  NC7SZ14 is comparable to most small mosfets ($0.06 in
> 1000, $0.13 in 100), input thresholds are nicely logic- like, output
> drive is somewhat smaller but sufficient for LEDs... Probably abuse-able
> without current limiting resistors on the outputs, even.  Thoughts?

I use the TI "Microgate" logic series quite often for LED drive buffers and
logic level conversion. The LVC and AHC series are quite versatile. I
mostly use the single and dual gate packages.

The LVC series has 5V tolerant inputs for interface between 5V peripherals
and 3V chips that aren't 5V tolerant or just need a buffer. The SN74LVC1G17
Schmitt Buffer can source/sink 24mA at 3.3V Vcc, for instance. The LVC
series will run from Vcc 1.65V to 5.5V. The AHC series is similar with a
somewhat lower output drive capability (8 mA). Both series have Icc levels
around 10 uA so I use them in battery powered applications quite a bit as
well.

Never used them without output limiting resistors to drive LEDs (nor would
I. Frankly I've never understood the logic of that -- it's bad design no
matter how you look at it. I can think of better ways to save a sub-penny
in my designs).

Most parts are sub $0.10 in 1000's and available in SOT-23 or SC70
packages. Nice parts.

Matt Pobursky
Maximum Performance Systems
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