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TCAN1044AV-Q1 を使用します。TCAN1044AV-Q1のドミナント時CANH-CANL電位差について

narumir
Prodigy 60 points

Part Number: TCAN1044AV-Q1

TCAN1044AVDDFRQ1ドミナント時のCANHとCANLの電位差について

 

・Vo(dom)をみると、typ値記載がありませんが、typ=(min+max)/2と考えてよいでしょうか？

　　※例：CANHtyp=(2.75+4.5)/2=3.625V、CANLtyp=(0.5+2.25)/2=1.375V

 

・ドミナント時の電位差バラツキtypとmaxは以下のように算出しましたがあっていますでしょうか？

↑特性より、

標準=(3.625-1.375)=2.25V、最大=(4.5-0.5)=4V

 

一方で、Vod(dom)特性をみると、これよりも小さい値になっています。

弊社計算条件では厳しく出てしまっている為、下記値を採用してよいのか確認させてください。

例:45Ω≦RL≦70Ω時のVod(dom)はmin1.4V、max3.3V

 

・ドミナント時のVod(dom)はRLの値によって変わりますでしょうか?

↑では45 Ω時1.4~3.3Vとありますが、例えばRLmin=40Ω~65Ωの場合、電位差はどのように考えればよいでしょうか?

 

以上、お手数ですが宜しくお願い致します

  • 0
    Prodigy 60 points

    TCAN1044AVDDFRQ1が支配的な場合のCANHとCANLの電位差

    ・Vo(dom)を見るとtypの値は記載されていませんが、typ=(min+max)/2と仮定してよろしいですか?

    *例: CANHtyp=(2.75+4.5)/2=3.625V, CANLtyp=(0.5+2.25)/2=1.375V

    ・支配時間における電位差変動のtypとmaxは以下のように計算されますか?

    ↑特性から、標準=(3.625-1.375)=2.25V、マックス=(4.5-0.5)=4V 一方、Vod(dom)特性を見ると、これよりも小さい値です。

    当社の計算条件は厳しいため、以下の値が採用できるかご確認ください。

    例:45Ω≤RL≤70Ωが最小1.4V、最大3.3Vの場合のVod(dom)

    ・RLの値によってドミナントのVod(dom)は変化しますか?

    ↑45 Ωで1.4〜3.3Vと書いてありますが、RLmin=40Ω〜65Ωの場合、電位差はどのように考慮すればよいのでしょうか? ご理解のほどよろしくお願いいたします。

  • 0 in reply to narumir
    TI__Guru 53555 points

    Hello,

    We are only allowed to correspond with posts made in English on this forum. Could you please re-post your question in English so we may assist with your question?

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Prodigy 60 points

    Potential difference between CANH and CANL when TCAN1044AVDDFRQ1 is dominant

    ・Looking at Vo(dom), the typ value is not listed, but is it correct to assume that typ=(min+max)/2?

    *Example: CANHtyp=(2.75+4.5)/2=3.625V, CANLtyp=(0.5+2.25)/2=1.375V

    ・Are the typ and max potential difference fluctuations in the governing time calculated as follows?

    ↑ From the characteristics, standard = (3.625-1.375) = 2.25V, max = (4.5-0.5) = 4V On the other hand, the Vod(dom) characteristics are smaller than this. Since our calculation conditions are strict, please confirm whether the following values can be adopted.

    Example: Vod(dom) when 45Ω≤RL≤70Ω is minimum 1.4V and maximum 3.3V

    ・Does the dominant Vod(dom) change depending on the RL value? ↑It says 1.4 to 3.3V at 45 Ω, but how should we consider the potential difference when RLmin=40Ω to 65Ω? Thank you for your understanding.

  • 0 in reply to narumir
    TI__Genius 15345 points

    Hello,

    An engineer is working on this question. Because of the holidays, TI E2E design support forum responses may be delayed through Jan. 3. Thank you for your patience.

    Best,

    Chris

  • 0 in reply to narumir
    TI__Guru 53555 points

    Hello,

    The differential dominant output voltage is specified across all temperature and supply conditions, so the typical values of these characteristics is not necessarily the average of the minimum and maximum values. For instance, I commonly see a differential output voltage on the CAN bus of 2.5V. The specification for the single-ended output voltages is similar as you would expect both outputs to be lower when the supply voltage is lower, which will have less overall impact on the differential voltage.

    We test our devices over the load range specified in the datasheet to ensure each device performs appropriately. Naturally, with a larger load (less differential resistance) the output voltage will be smaller. Because the range of 40-ohms is not typical for a CAN system, this is not included in our test plan or datasheet.

    Let me know if you have any more questions. 

    Regards,
    Eric Schott 

  • 0 in reply to Eric Schott1
    Prodigy 60 points

    The CAN driver is powered by a linear regulator. The higher the dominant current, the higher the losses in the linear regulator. Therefore, I would like to estimate the maximum current at dominant time by calculation. Since Vod is 1.4V to 3.3V when RL=45Ω to 70Ω, I think the maximum current = 3.3V/45Ω = 73mA, is that correct?

  • 0 in reply to narumir
    TI__Guru 53555 points

    HI Narumir,

    This is one method to do the calculations. However, we characterize this behavior of our device directly with the ICC specification. In this case with a 50-ohm load, the maximum current draw from the Vcc pin will be 80mA. With a lower resistance between CANH and CANL, I would expect the 40-ohm case to have a slightly larger maximum current. Use this value for maximum estimated power use during normal dominant operation. For maximum thermal or peak power calculations, I recommend using the "dominant with bus fault" specification of 130mA. Note that this value is not dependant on the differential load since it is the current limit of the driver itself. 

    Regards,
    Eric Schott 

  • 0 in reply to Eric Schott1
    Prodigy 60 points

    If the formula below is incorrect, please tell me why. Dominant maximum current = 3.3V/45Ω = 73mA (RL=45Ω to 70Ω) The data sheet says max80mA, Please tell me the main reason for the difference from the value calculated by the above formula.

  • +1 in reply to narumir
    TI__Guru 53555 points

    Hi Narumir,

    The formula is correct, but it doesn't account for all variables that impact current draw. For instance, the transceiver itself draws some quiescent current independent of the bus load. Our characterization of the device for the listed specifications includes all of these factors as well as margin for operating conditions and process variation. 

    Regards,
    Eric Schott