SN74LVC2T45-Q1: Hardware review

Intellectual 840 points

Replies: 2

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Part Number: SN74LVC2T45-Q1

Hi Manuel,

I have updated the design, Please find it in the attached file.



Total 2 Digital input with 12V inputs and One Digital output with 5V output level.

1. Whether the design is sufficient?

2. 12V supply is Isolated but the 5V supply is Isolated as shown in the circuit, and shorted the Isolated and External GND(12V supply GND) together, will this work?

3. Or 12V also should be isolated?

Please suggest.

Kindly support on priority.


2 Replies

  • Please note our MCU accepts only 1.8V logic level.

  • [Same answer in the isolators forum.]

    The R34/R35 voltage divider does not generate a valid logic level. To set the B→A direction, drop R34; but you can connect DIR directly to GND.

    Unidirectional downtranslation can be done with a buffer with overvoltage-tolerant inputs; you can replace U21 with a SN74LVC2G17-Q1.

    CMOS inputs must not float; ground pins C and D of U22.

    These three level shifters do not support isolated power supplies and require a common ground on both sides. And when you do connect all the grounds together, isolating the power supplies is pointless. If you do require isolation, then you must also isolate the three signals with a real isolator like the ISO7731-Q1. (It cannot go below 2.5 V or above 5 V, so you still need the level shifters.)