| Electronics > Projects, Designs, and Technical Stuff |
| DIP version of voltage level converter SN74LVC1T45 ? |
| (1/6) > >> |
| FrankBuss:
I'm searching a DIP part which does the same as the SN74LVC1T45. I need to do voltage level translation between 3.3 V and 5 V and the other direction. For 5 V to 3.3 V I tried to use a resistor divider with 3.3 k and 2.2 k, but the edges look terrible at 8 MHz, and it should work up to 20 MHz. For the other direction I tried this circuit, but it was not that fast, too, because of the high pullups. Is there a solution with only DIP parts for both translations? The direction is fixed for each translation, but I need a solution for each direction. I'm planning to interface an Atmega328 with a SPI flash or FRAM chip, and my client wants to release it as a DIY kit with through hole parts, only. |
| T3sl4co1l:
Use lower value resistors, and use 74HCT family receivers to go the other way. Or just use 3.3V to begin with. Almost everything available today supports it! 74LVC is basically useless in DIP. If you can only find SOICs of them, and nothing else with the same function, consider learning SMT. SOIC is only half pitch, it's quite easy to deal with. :) Tim |
| FrankBuss:
The Atmega328 needs to run at 20 MHz, which is not supported at 3.3 V. I would use all SMD parts, but my client insists on having it all in through hole. Maybe I could use lower resistors, but maximum output current is 40 mA per pin, but this is the absolute maximum rating, and output voltage drops already to like 4.5 V at 15 mA, and the supply voltage could be a bit lower than 5 V as well (USB power supply powered). Maybe it would work, but this is how it looked at 8 MHz (yellow trace) : And I want to use the SPI bus at 20 MHz, so I don't think the resistor divider would be a good solution. I don't mind using some discrete external parts like MOSFETs or transistors, but I'm not an analog expert, I have no idea how this would look like for this high speed. |
| T3sl4co1l:
Well, not guaranteed at 3.3V. If you don't need 100% yield, you can consider overclocking it. Sounds like you've worked yourself into a bit of a corner. Have you considered a different clock frequency? Faster MCU (XMEGA say)? Why does it have to be AVR at all, if you need hard real-time performance? Why not an ARM at 80MHz+? (They're far more powerful, and just as cheap. Internal USB support is common, too.) Tim |
| oPossum:
74HCT for 3.3 to 5 volt. 74AHC for 5 to 3.3 volt 74xx244, 74xx125, etc... |
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