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SN65HVD1050: Current consumption

Michiaki Tanii
Expert 4610 points
Part Number: SN65HVD1050

Hi team,

 

Could you kindly advise the Icc in the below conditions?

 

<Customer’s conditions>

-        Node                           30

-        Termination                120 ohm (both end of the bus)

 

<Questions>

-        Is the Icc of receiver node same with the Icc of recessive mode ? Only one device in the CAN bus transmit data.

-        What situation is the most largest current consumption at 30 node ?
When all the devices in the CAN bus transmit ACK is largest ? or other conditions ?
Customer would like to make sure not only for IC but also total current consumption in the CAN bus.

 

Thank you and best regards,

Michiaki

  • 0
    TI__Guru 62920 points

    Hello Tanii-san,

    Yes, a node that is receiving data will primarily be in the recessive state and so it's ICC would match the recessive-state IC.  There will be a brief exception at the end of a frame where each node sends a dominant bit in order to acknowledge the frame.

    Yes, under normal operating conditions (i.e., no short circuit faults) the total ICC would be highest during cases where all transmitters are active simultaneously.  However, the current will not be as bad as the normal per-transceiver dominant ICC multiplied by the number of transceivers.  This is because the transceivers all act in parallel and the current required to drive the dominant level is spread between them.  You could consider the upper limit of ICC in this case to be VCC / Rterm where Rterm is the total differential resistance of the bus (typically 60 Ohms for CAN) plus the sum of the recessive state ICC of each node.  The first term would encompass the shared driver output current while the second terms could be considered a kind of quiescent current for each transceiver (i.e., the current required to power internal circuitry besides the output driver).  Please let me know if this is not clear.

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    TI__Expert 4610 points

    Hello Max,

     

    Please let me double check our understanding.

     

    Can customer estimate the total power consumption as the below ?

     

    1. The number of node x recessive current (max 10mA)
    2. Dominant driver : 83mA ( 5V / termination resistor 60 ohm)

     

    If the number of node is 32, can the total power consumption be estimated as below ?

    32 x 10mA + 83mA = 403mA

     

    Customer think that total power consumption would be larger than the above at the moment that all the drivers return ACK.

    If yes, how much total power consumption would be larger ?

     

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Guru 62920 points

    Michiaki-san,

    Your understanding is correct.  I can understand that because the dominant-state ICC of a single transceiver is at most 70 mA, the customer may expect the total current when all nodes ACK to be something closer to 32 x 70 mA.  But, this current is primarily what is needed to drive a voltage across the bus impedance (60 Ohms).  Because a CAN driver is unable to drive CANH higher than VCC or CANL lower than GND, the upper limit on current flowing to the bus is VCC / 60 Ohms.

    Regards,
    Max