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SN74LVC2T45-Q1: Hardware review

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Replies: 5

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Part Number: SN74LVC2T45-Q1

Hi Manuel,

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

GPIO's.pdf

For GPIO

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.

Manjunath

  • 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.)

  • In reply to Clemens Ladisch:

    Hi Manuel,

    Please find the attached updated design.

    1070.GPIO's.pdf

    1. 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.

    Manjunath : Noted.

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

    Manjunath : "SN74LVC2G17-Q1" doesn't do voltage translation from 5V to 1.8V.

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

    Manjunath : Thanks Noted.

    4. We are currently looking for Digital Isolators for our apllications.

    i. We need to isolate 2 Digital inputs whose digital lines voltage will be 12V

    ii. and One Digital output whose voltage levels is 5V

    iii. Main MCU accepts only 1.8V level.

    So, for Digital inputs, Considering from Outside world, first I need to regulate the 12V levels to 5V levels and then I need to Isolate it and then again should do the voltage translation to 1.8V. I'm I right here?

    For Digital Output, I need a Isolation and then Voltage translator to 1.8V.

    Please check the attached schematic and review the same.

  • In reply to Manjunath G14:

    Hi Manjunath,

    For Question 2, yes that device can down translate 5 V to 1.8 V. For everything regarding isolation devices I will move this thread over to the respective product line. 

    Check out our new AXC family of Voltage Translators! 

    Watch the Introduction to AXC Family to find out more about the family.

  • In reply to Dylan Hubbard:

    Thanks Dylan!

    Hi all,

    This discussion is being continued in the thread below:



    Thank you for posting to E2E!


    Respectfully,
    Manuel Chavez