From: Winfield Hill
Subject: Re: Design for long interval timer
Date: 4 Dec 2002 07:44:22 -0800
Organization: Rowland Institute
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Fred Bloggs wrote...
> Spehro Pefhany wrote:
>> for a timer.. consider using the MC14541.
> Hmmm...a few problems with one:
> 1) ON is dropping products left and right;
The availability of '4541' timer chips is certainly as safe to rely
on as any IC. It's a popular, venerable design, widely stocked at
good prices, and manufactured by five companies: Philips, TI, ST,
Fairchild, and ON Semi. I'd probably buy an ON Semi IC, because
Motorola originated the design.
> 2) the "exploded logic diagram" is clearly in error regarding the
> MODE control logic;
Use another vendor's data sheet if that bothers you. TI's data
sheet (acquired from Harris = Intersil) has a good description.
Of course one should always use the data sheet's Truth Table or
Function table if in any doubt.
> 3) the AUTO RESET only works for Vdd above 8.5V;
"The AUTO RESET consumes an appreciable amount of power and should
not be used if low-power operation is desired." Careful designers
would consider avoiding use of a 'black-box' reset circuit anyway.
The 4541 design has much to recommend it, hence its over 30 years
of popularity. Most of us have used it successfully for a variety
of tasks in some of our designs.
Thanks, Spef for the suggestion and reminder.