Unpowered ADM3053

In the features list of the ADM3053 on the first page of the datasheet, it is mentionned that unpowered nodes do not disturb the bus but in table 10, the bus state is indeterminate with Vio On, Vcc Off and TxD Low which to me means that it can force a dominant state on the bus.

In my system, I need to unpower both the Vio and Vcc nodes for energy saving without disturbing the bus. Is it possible with the ADM3053 ?

What is the bus state in the following conditions ?

  • Vio OFF, VCC OFF and Txd HIGH or LOW
  • Vio ON, VCC OFF and TxD HIGH
  • 0
    •  Analog Employees 
    on Feb 23, 2012 8:00 PM

    You can power off the ADM3053 on both Vio and Vcc without disturbing the bus.

    With Vio off, Vcc off and TxD high or low, the outputs of the ADM3053 will not affect the bus. With Vio on, Vcc off and TxD high, the same applies. The ADM3053 will not force a dominant state on the bus in any of those cases.

    The indeterminate in the truth table refers to the bus state not being affected by the unpowered node, even if TxD is low (but the bus state is unknown as it is dependent on other nodes).

  • I have replaced a mcp2551 CAN chip with a small piggyback board containing an ADM3053 and some components. I turn the ADM on/off via the RS line (used before by mcp2551) but this line controls the power via a power switch on this little board. A low voltage on RS line brings 5V to Vio and Vcc. During the turning off (RS becomes high) the power switch opens and the Vio=Vcc voltage drops slowly. I can also see the VISOout drop even slower. At a certain moment I see a spike on the CAN bus (dominant). This pulse is 3 usec long.

    Could this disturbance be explained somehow?

    Does the chip contain any reset levels on the power voltages?

    Or better how should we properly power down/up the device without CAN disturbance?

    Unfortunately I have no development board from AD to test it.