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SN65HVD3082E: Application in air conditioner

Part Number: SN65HVD3082E
Other Parts Discussed in Thread: THVD1500, SN65HVD888, SN65HVD1794, THVD1419, THVD2410

Hi team,

I have noticed that SN65HVD3082E has win in the Air conditioner. So I have some question for that:

1. What kind of spec of the RS485-TRX would the customer care in the application of air conditioner?

2. Why the SN65HVD3082E could be the hero device in the air conditioner? what's the advantage of the SN65HVD3082E comparing with the competitor?

I will appreciate your answer.

Best Regards,

Wesley Huang

Email: wesley-huang@ti.com

  • Hi Wesley,

    One thing that is common for many HVAC applications is that they could involve a large number nodes operating at lower data rates but communicating over relatively long distances across cabling networks that are not ideally routed (due to building constraints).  The SN65HVD3082E's driver slew rate control is beneficial in this case since it allows for the needed data rates to be supported but helps to reduce signal integrity issues that might arise in some applications due to the presence of unterminated "stub" connections in the wiring.  You could learn more about this sort of concern via this video:

    https://training.ti.com/ti-precision-labs-rs-485-best-practices-implementing-rs-485-transmission

    That said, a newer device which is p2p with SN65HVD3082E would be the THVD1500.  This device is similar in functionality but improves the ESD immunity which helps to make for a more robust end solution (reducing issues like field failures / customer returns).  I would generally recommend this device for new designs over SN65HVD3082E.

    Both of these devices are "basic" RS-485 transceivers for cost-sensitive applications that do not implement additional features or very high levels of protection (besides the THVD1500's IEC ESD performance).  In many HVAC applications, though, more features are needed.  For example, some users want the ability to correct for mis-wirings which could occur by technicians in the field.  The SN65HVD888 device can help here by automatically sensing a swap of the A/B lines and correcting for it.  The SN65HVD1794 is also able to invert the signal polarity to correct for this but can withstand up to +/-70 V on the signal lines as well - this is useful in cases where short-circuits between the RS-485 signals and higher voltage power lines are possible.

    Also, some applications may need to withstand higher transient surge currents (such as those defined by IEC 61000-4-5).  In these cases a TVS diode may be used on the PCB.  As an alternative, though, the THVD1419 device could be used.  This integrates a TVS capable of withstanding 2500-v surges, eliminated the need for an external TVS.  This can help reduce system component count and PCB space.  You can read more about this feature in the following technical article:

    https://e2e.ti.com/blogs_/b/analogwire/archive/2019/03/29/can-your-rs-485-communication-survive-the-great-outdoors

    I hope this is all clear - please let us know if you have any questions.

    Regards,
    Max

  • Hi Wesley,

        One more RS-485 transceiver that good for HVAC is THVD2410. It is a 3.3V to 5V supply, 0.5 Mbps half-duplex RS-485 transceiver with +/-70V bus fault protection, 12kV built-in IEC 61000-4-2 ESD protection, and +/-25V common mode voltage range. The bus fault protection can prevent transceiver short-circuit up to 70V. Wider common mode voltage range works over greater ground potential differences for long cable communication. 12kV built-in IEC 61000-4-2 ESD protection helps to improve system level reliability and robustness. THVD2410 is a good part used in HVAC.

    Thanks and best regards,

    Kankan Wang

  • Hi Max,

    Thanks for your reply. I haven't found the passage about the slew rate control in the datasheet of SN65HVD3082E.

    Could you please point out the chapter for me?

    Best Regards,

    Wesley Huang

    Email: wesley-huang@ti.com

  • Hi Kankan,

    Thanks for your reply.

    Best Regards,

    Wesley Huang

    Email: wesley-huang@ti.com

  • Wesley,

    The slew rate limiting is evident based on the rise time (tr) and fall time (tf) specifications in the driver switching characteristics table.  The impact of these rise/fall times on network topology is described in Section 9.2.1.2.  In short, greater slew rate control gives longer rise/fall times which allow for longer unterminated stubs on a network before significant signal integrity impairments are observed.

    Regards,
    Max