SN74LVC8T245: Direction Controlled Replacement for TXB0106

Kevin Allen18

Part Number: SN74LVC8T245
Other Parts Discussed in Thread: TXB0106, SN74AHC541

Hi Experts,

I'm working through a new design and am looking to replace the auto bi-directional level translator device used in the previous design (TXB0106) with a comparable direction controlled device. I have come across the SN74LVC8T245 device which looks like it may be a good option, but would like your input before settling upon it. Only 6 channels are needed, so 2 of them on the 8-bit SN74LVC8T245 device would not be used and left unconnected.

In the design, side B will be a 5V level input to the device coming from a quadrature encoder. Side A will be a 3.3V level output going to a C2000 MCU purposed for its quadrature encoder peripheral (eQEP).

Please let me know your thoughts on this and if you have any suggestions. I can provide schematic images for clarity as well if needed.

Thanks,

Kevin

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316440 points

This level shifter will work. However, when all signals go into the same direction and are to be shifted down, then you can simply use any buffer with overvoltage-tolerant inputs, e.g., SN74AHC541.

Unused CMOS inputs must not be left unconnected.

0 Kevin Allen18 over 5 years ago in reply to Clemens Ladisch

TI__Mastermind 45046 points

Hi Clemens,

Thank you for your reply and mentioning the unused connections. I had missed that and will tie unused channels to GND or PWR.

The SN74AHC541 seems like it would be a good option. Reviewing the datasheet it looks like it can step down signals ranging from 2V - 5.5V down to 3.3V without needing a separate supply voltage, is that correct? That would be good to have in the case where a 3.3V encoder is used instead of 5V.

Below is a snip from my schematic, would appreciate if you get a chance to take a look. 3.3V will be the MCU power.

Thanks

Kevin

0 Clemens Ladisch over 5 years ago in reply to Kevin Allen18

Guru 316440 points

Looks fine.

Only inputs need to be connected; unused outputs can be left open.

Logic

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SN74LVC8T245: Direction Controlled Replacement for TXB0106