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SN65HVD72: RS485 Wake Up from Sleep

Michael Veenstra
Prodigy 10 points
Part Number: SN65HVD72
Other Parts Discussed in Thread: MAX3223

Tool/software:

In general, it seems these RS485-to-UART converters have a standby/shutdown mode with low current BUT only when the device is fully disabled. This is great for my battery powered application, except how do I know it's time to turn it back on? Is there a standard external "sniffer" type circuit that can monitor the data on the lines and then trigger an interrupt on my MCU to tell it to enable the RS485 again?

I have a RS232-to-UART (MAX3223) that has an auto-powerdown that can detect when data is incoming and turn back on. Is there a solution that achieves similar results for RS485?

  • 0
    Guru 283350 points

    RS-485 is usually used for industrial application where power usage is not a large concern.

    It might be possible to read the bus voltages with comparators, but when you need to support the entire bus voltage range, this would be hard to do, especially with less than 0.6 mA. Also, the receiver enable time of up to 8 µs might be too long.

  • 0
    TI__Expert 4736 points

    Hi Michael,

    Below I have highlighted the time required for the device to turn on from the low power mode:

    For instance, if both receiver/driver are disabled, then turning on the driver or receiver takes around 3 us (9us maximum). 

    We currently do not have an RS-485 device that automatically powers on based on incoming data.

    Regards,

    Ethan