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AM26C31: Power dissipation details

Vinith S
Prodigy 20 points
Part Number: AM26C31

Hi,

  1. We are using AM26C31 part for our applications. We use baud rate of 115200. In datasheet,there is a graph detailing about switching frequency vs supply current. From the graph,it is noted that for 115200,supply current will be 120mA when all the four channels are operating simultaneously. So power dissipation in IC will be 120mA*5V = 0.6W. Is this correct whether IC will consume 120mA for 115200 baudrate? Also please clarify whether any other power dissipation factor also to be considered or only 0.6W dissipation.
  • 0
    Guru 244360 points

    Cpd is specified as 170 pF, so I guess that graph uses a wrong unit, and it should actually be 120 µA.

    Please note that this does not measure the much larger current that is sent through the bus. However, the power dissipation is shared by the driver transistors and the termination resistor (in the worst case of VOD = 2 V, the remaining 3 V × 20 mA are dissipated inside the driver).

  • 0
    TI__Mastermind 48215 points

    Hi Vinith,

    This is a rare occasion where I disagree with Clemens. The 120mA draw sounds correct for driving this frequency at the given load. This represents the total current through the supply pin under these conditions, not just the added draw from capacitive losses.

    As Clemens points out, not all of this power is dissipated in the transceiver as most of the voltage drop on the DC current path occurs across the termination resistor. For thermal calculations, the power dissipated in the termination resistor should be considered separate from IC power consumption. 

    Let us know if you have any more questions.

    Regards,
    Eric Schott