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TCA9517-Q1: pull-down

ssatake
Prodigy 40 points

Part Number: TCA9517-Q1
Other Parts Discussed in Thread: TCA9517, SN74LXC1T45

5Vと3.3Vの双方向レベル変換に「TCA3-Q3」を使用することを検討しています。プルダウン抵抗を3.3Vシステム入出力端子に挿入し、プルアップ抵抗を5Vシステム入出力端子に挿入します。電源投入時にローレベル(0V)に設定したいのですが。質問は次のとおりです:
1.「TCA9517-Q1」の使用に問題はありますか?
2. プルダウン抵抗値の計算方法を教えてください。

  • 0
    Guru 321490 points

    The TCA9517-Q1 is designed for I²C, so it uses open-drain signals and requires pull-up resistors on both sides.

    What is "TCA3-Q3"?

  • 0
    TI__Guru 58358 points

    Hi Ssatake,

    Please elaborate on what you mean by TCA3-Q3. 

    What are you trying to do with the pull-down resistor on the TCA9517-Q1? The 9517 uses internal buffer drivers to re-drive the I2C signal to a low logic. Pull-ups are required in order for the signal to rise back to logic high voltage. Why do you need to pull-down an input upon startup of the 9517? 

    The supply voltage range from 3.3V to 5V will work for the TCA9517. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 40 points

    [TCA-Q3] はタイプミスです。正しい名前は "TCA9517-Q1" です。
    I2C には使用されません。SDI-12レベル変換に使用できますか?それが私が考えていることです。

  • 0 in reply to ssatake
    Guru 321490 points

    It is not possible to use an auto-bidirectional translator for the SDI-12 data line.

    You need a direction-controlled translator like the SN74LXC1T45. If your MCU uses separate input and output pins, add a series resistor at the output so that the MCU does not conflict with the A pin when the direction is B to A.

  • 0 in reply to ssatake
    TI__Guru 58358 points

    Hi Ssatake,

    In addition to Clemens comments, what is the voltage level of the serial data line in your SDI-12 application? Is the 12 volt line required in SDI-12 also a factor when using the TCA9517? 

    Regards,

    Tyler