| Electronics > Beginners |
| Logic Level Shifters? |
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| theatrical scene:
I'm working on a project which uses 3.3V from a Raspberry pi with 5V peripherals. I only need to send/receive data in one way (so the logic level shifter wouldn't have to be bidirectional). I'm choosing between these two parts: http://www.ti.com/lit/ds/symlink/cd4050b.pdf and http://www.ti.com/lit/ds/symlink/txb0108.pdf. Is the latter component overkill for simple digital IO conversion? I assume a standard buffer like the first component would be able to shift up signals if I supplied 5V to VCC with a 3.3V input signal but the data sheet has no mention of this and rather highlights the 4050B's use as a 'high to low' shifter as opposed to low to high. Is my assumption valid or am I missing something? Cheers |
| oPossum:
CD4050 is only for 5V to 3.3V (74AHC series can also be used). For the other direction 74HCT series parts can be used, such as 74HCT244 and 74HCT125. |
| theatrical scene:
Low bandwidth (around 20KHz), delay budget not too critical, no restrictive cost requirements (within reason), bus width of 6-8. |
| Mr.B:
When I am level shifting I2C (bus width = 2) I simply use a couple of cheap FETs and a few resistors. Dead simple. Google *FET level shifter* |
| theatrical scene:
--- Quote from: oPossum on January 22, 2019, 12:28:22 am ---CD4050 is only for 5V to 3.3V (74AHC series can also be used). For the other direction 74HCT series parts can be used, such as 74HCT244 and 74HCT125. --- End quote --- Thanks for that, will have a look. The RPi has uses both inputs and outputs which means I would need to get both the 74HCT and 74AHC parts right (for low-high level shifting and high-low)? Would it make it easier to just use a single bidirectional converter like the TXB0108 even though my signals are unidirectional (i.e. either outputs or inputs)? |
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