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SN65HVD234 Sleep Mode

Shahzad Malik97479
Intellectual 295 points
Other Parts Discussed in Thread: SN65HVD234

I'm using the TI SN65HVD234 CAN XCVR which we use on several of our products.  I want to use the SLEEP mode for minimum supply current, and the data sheet says that I must set EN to 0 and D to VCC.  If there is a voltage on the CAN bus from some other node, will this affect the sleep mode supply current?  Currently, the part powers up with RS held at VCC, so I believe that the part is guaranteed to be in the recessive mode until Rs goes below 0.33 Vcc.  I've seen no problems with this, but I want to make sure I don't cause one by using the EN pin, which is currently held to Vcc.

  • 0
    TI__Mastermind 21543 points

    Hi Shahzad,

    The reason the device says to put D at VCC, is because there is a pull-up resistor on this pin. Therefore, the device will have a lower system power if the pin is help high.

    With the RS pin tied high, the driver will be powered off. Therefore, the loading on the bus will be due to the receiver which is found on page 6 of the datasheet. We specify a maximum of 610µA which occurs at the minimum standoff voltage of the device (-7 volts on the bus pins with the device powered off). This current will be a sinking current which will be drawn from the other nodes on the bus to ground. With that being said, if the device is powered on and the receiver is on we specify up to 6mA of current draw.

    I am not sure if I fully understand your question. If the device is powered up and in Sleep mode, the sleep current specified is across normal operating conditions.

    Please let me know if I didn’t answer your question, or if you have any others.

    Thanks,

    John

  • 0 in reply to John Griffith
    Intellectual 295 points
    I want to use the SLEEP mode to reduce the device idle current.  My concern is that if there is a voltage on the bus (from another node), it might cause the SN65 to do something weird, like coming out of SLEEP mode, or load the bus improperly.  With EN pulled low, both the driver and receiver should be powered OFF, so I expect a supply current of no worse than 2uA. 
    The other alternative that I considered was to remove VCC from the part when the module is idle, but I worry that an unpowered part might do something unexpected.  There's nothing in the spec to cover this situation, so the SLEEP mode seems to be a safer choice. 
  • 0 in reply to Shahzad Malik97479
    TI__Mastermind 21543 points

    Hi Shahzad,

    I agree you are better off have the device powered and in SLEEP mode since this behavior is characterized. Your local node supply current will be very low, 50nA typical and 2µA maximum.

    The bus pins however will still cause some loading on the bus, as defined by the table on page 6 of the datasheet. This loading will need to be considered with respect to the total number of nodes you plan to have on the network and the length of the network you plan on having.

    Thanks,

    John

  • 0 in reply to John Griffith
    TI__Mastermind 21543 points

    Also, these products are all supported in the industrial interface forum (link below), so I am going to move this thread to the appropiate forum.

    http://e2e.ti.com/support/interface/industrial_interface/f/142.aspx

    Thanks,

    John