Author Topic: MAX 7000S driving 5V Logic  (Read 597 times)

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Offline NivagSwerdnaTopic starter

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MAX 7000S driving 5V Logic
« on: February 14, 2019, 11:48:29 am »
In the context of 1980s Arcade game PCBs...

I'm contemplating having a go at replacing some custom logic with a MAX 7000S device which appears to be pretty cheap on ebay (despite being obsolete).  If I drive the device at 5V I see that in order to drive 5V CMOS outputs that an external pull-up resistor is required, I even found an application note: http://extras.springer.com/2001/978-3-662-04615-9/an/an107.pdf

How am I meant to calculate RExt? 10k 47k?

EPM7128SLC84-15 is the device of choice.

Thanks in advance,


 

Offline edgaras006

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Re: MAX 7000S driving 5V Logic
« Reply #1 on: February 14, 2019, 12:58:45 pm »
From load capacitance and required switching frequency. Since it uses only nMOS logic, for +5V output you need a pull up resistor. R = 1/(2*pi*Cload * F switching). On the other hand, RC should be approximately 1/10 of switching frequency. Side note if you reduce R too much you might hit n most current limit, so watch out for that.
 
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