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SN65HVDA1040A-Q1: Driver Bus Output Voltage vs Output Current

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Replies: 5

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Part Number: SN65HVDA1040A-Q1

Hello,

Are any curves on driver bus output voltage (dominant) VO(D) (both CANH and CANL) vs its output current of SN65HVDA1040A-Q1 with different loads available? I'd like to estimate driver CANH and CANL voltages with loads apart from the data sheet condition of RL = 60 Ω. Especially, I'd like to know how much the driver CANH and CANL voltages will change when the RL goes down to 44 and 32 Ω.

Best regards,
Shinichi Yokota

  • Yokota-san,

    These aren't available right now, but we can take these measurements in the lab if you need them. Some of our newer TCAN devices show the VOD(D) down to 45 ohms, but nothing on the older SN65HVDA1040A-Q1. I'll take the data and update tomorrow when I have the results.

    Regards,

    Eric Hackett

    Texas Instruments | INT-TRX| Applications Engineer

  • In reply to Eric Hackett:

    Eric-san,

    If it's not trouble for you, could you take some measurements with a couple of units? It would be helpful if the data is taken with some RL between 60 Ω, the data sheet's test condition, and 32 Ω, too.

    Regarding the Max-Min variation of the VO(D) (CANH and CANL respectively) with different RL, is it OK to say the data sheet specs, -15% (2.9 V) and +32% (4.5 V) from the Typ 3.4 V at RL = 60 Ω, can be applied to other RL, too?

    Best regards,
    Shinichi Yokota

  • In reply to Shinichi Yokota:

    Yokota-san,

    Thank you for your patience on this. I measured across 3 units at room temperature.

    RL = 44ohms

    Unit 1: VO(D) - CANH = 3.16V, CANL = 1.18V

    Unit 2: VO(D) - CANH = 3.2V, CANL = 1.2V

    Unit 3: VO(D) - CANH = 3.16V, CANL = 1.22V

    RL = 32ohms

    Unit 1: VO(D) - CANH = 2.98V, CANL = 1.36V

    Unit 2: VO(D) - CANH = 2.94V, CANL = 1.31V

    Unit 3: VO(D) - CANH = 2.97V, CANL = 1.35V

    Because the variation is heavily dependent on the load resistance of the bus, I don't think it can be assumed that the same variation will apply to all other load resistances. This can be seen in the VOD(D) parameter in the datasheet, where multiple RL are tested, and the voltage range changes based on the load resistance.

    Regards,

    Eric Hackett

    Texas Instruments | INT-TRX| Applications Engineer

  • In reply to Eric Hackett:

    Eric-san,

    Thank you very much for the data. But I have a quick question.

    In open-drain configuration of transistor circuit, VDS increases as ID goes up given VGS is constant, but the result of CANL voltage shows an opposite direction. The CANL voltage with RL = 44 Ω is around 1.4 V while it's roughly 1.3 V with RL = 32 Ω. Can you give me a comment from this transceiver's architectural point of view?

    Best regards,
    Shinichi Yokota

  • In reply to Shinichi Yokota:

    Yokota-san,

    You are correct, I just re-checked the voltages. I must have incorrectly measured using the oscilloscope when reading the 44 ohm termination values. The 32 ohm termination voltages remain the same. I've edited my previous post to show the correct values for 44 ohm termination.

    Regards,

    Eric Hackett

    Texas Instruments | INT-TRX| Applications Engineer

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