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SN65HVD1780: Inquiry for 3.3V application

Renan Santos Adriano
Mastermind 19085 points
Part Number: SN65HVD1780
Other Parts Discussed in Thread: THVD2410, THVD2450

Hello Team,

My customer needs confirmation about the device SN65HVD1780 in a 3.3V supply. They wanted to confirm if can the transceiver still have up to 320 nodes with only a 3.3V power supply? In the datasheet, it says up to 320 node, but they assume this is for a 5V power supply. The datasheet says, "These devices are fully compliant with ANSI TIA/EIA 485-A with a 5-V supply and can operate with a 3.3V supply with reduced driver output voltage for low-power application"

Thanks in advance.

Regards
Renan

  • +1
    Guru 278840 points

    The RS-485 specification requires that the driver outputs at least 1.5 V. The |VOD| specification shows that this is not the case at 3.3 V.

    The RS-485 specification requires that a receiver can cope with at most 0.2 V. Figure 3 shows that the SN65HVD1780 at 3.3 V still outputs more than that, but that you have a reduced noise margin.

    Reducing the number of nodes will not have much of an effect; two 120 Ω termination resistors are the same load as 200 unit loads of 12 kΩ.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 25705 points

    Renan,

    Please check out THVD2450/THVD2410 if you need high fault voltage. Considering DC loss only, this device can work with up to 256 nodes. 

    Regards,