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DIP version of voltage level converter SN74LVC1T45 ?
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TK:
Why not use ICs made specifically for digital level shifting like TXB0104 or a level shifting solution using FET transistors?
FrankBuss:

--- Quote from: OM222O on April 11, 2019, 12:05:53 pm ---Edit: voltage on the inputs does not matter at all. there is no specification on it whatsoever. only maximum current rating which is +-20mA. keep that in mind.
in terms of note from manufacturer look at page 9:


m the family you want, 99.9% of your questions are already mentioned there

--- End quote ---

Thanks, looks like the 74HC04 can be used for the 5 V to 3.3 V conversion, if powered with 3.3 V. But I still think it would be too slow. And it won't work reliable for the other direction, because at 4.5 V the high level input voltage is min 3.15 V. This is a very low margin to the 3.3 V output of the flash. And for 6 V it is even 4.2 V, so for 5 V supply voltage it would be right on the edge of 3.3 V.

My solution is to use http://www.ti.com/lit/ds/symlink/sn74ahc125.pdf for 5 V to 3.3 V, and http://www.ti.com/lit/ds/symlink/sn74ahct125.pdf for 3.3 V to 5 V. They don't break the bank either for less than $0.50, no need to design a $20 circuit :) I will buy some of these chips and will post some tests, and I will buy a 74HC04 as well to compare it.


--- Quote from: TK on April 11, 2019, 12:24:39 pm ---Why not use ICs made specifically for digital level shifting like TXB0104 or a level shifting solution using FET transistors?

--- End quote ---

The requirement of my client is to use only DIP chips. I don't think that the TXB0104 is not available in DIP. If SMD would be allowed, I would use the SN74LVC1T45, which I already used in other circuits like my Crazy Cartridge and it worked fine.

A solution with FET transistor would be fine, too, if it works for 20 MHz. But I don't know how this looks like, because I don't know much about analog electronics. And I guess would need more parts than the solution with the 2 ICs I've selected and more expensive, if assembly costs per part are also counted.
Zero999:

--- Quote from: FrankBuss on April 11, 2019, 12:25:59 am ---If I use a 10 k series resistor, then it could be too slow.
--- End quote ---
How about bypassing the resistor with a suitable capacitor to speed it up?

If the capacitance of the input is known, then the capacitor can be chosen so it translates 5V to 3.3V at AC, with the resistor not contributing to the voltage conversion.
OM222O:
if you want purely speed, you can even use BJTs in DIP packages and make the gates using some external resistors. 2 BJTs would still be suitable for >1GHz  :-//
you just need to choose your values so you won't exceed their current / voltage limits which should be simple at logic levels of 5 or 3 volts  :P

something like below, and depending on whether you power it from 3.3 or 5 volts, it can do up / down conversion and again, it is fast enough for GHz range. calculating base resistor and emitter resistors should also be a trivial task.


edit:
sparkfun uses the exact same topology for their level shifter modules (although they use fets which makes it much slower than BJTs, but it's the same idea):
https://www.sparkfun.com/products/12009
searching for bjt level shifter you can find this:


or a bidirectional one here: http://saeedsolutions.blogspot.com/2013/07/bidirectional-buffer-circuit-using.html
FrankBuss:
I got the ICs I selected, thanks to the initial suggestion from oPossum, and did some tests, and compared it with the 74HC04 as well:

https://hackaday.io/page/6095-voltage-level-translators

The 74HC04 might work, but the other ICs are a little bit faster, and for the 3.3 V to 5 V translation, the 74AHCT125 works with lower input voltages, guaranteed by the datasheet, so I will use these ICs. Should be no problem for the 20 MHz SPI clock.
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