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SN65HVD3083E: Preparing Power source

na na78
Guru 16770 points
Part Number: SN65HVD3083E

Hi

I'm considering power source for SN65HVD3083E.

As the power dissipation of IC itself, we can refer 136mW as maximum from datasheet.

So, if VCC is 5V, the current of IC would be calculated as 136mW/5V = 27.2mA as maximum.

However, I think it does not include device output power. 

So as additional consideration, I think I would need to add output current.

Using DRIVER ELECTRICAL CHARACTERISTICS, Iout can be calculated as 42.6mA when VOD=2.3V and RL=54ohm.

So if in this condition, we would need 27.2mA + 42.6mA = ~70mA as total current capability for SN65HVD3083E.

As a result, we consider 5V/100mA power source should be enough to operate SN65HVD3083E.

Is my understanding correct?

BestRegards

  • 0
    TI__Guru 62910 points
    Hello,

    You are correct that the power dissipation from the IC would not include the power delivered to the load resistance on the bus, and so your idea to use the VOD and load resistance value in order to compute the total supply current makes sense. You may also want to consider the maximum short circuit output current as well if your application requires the power supply to remain in regulation in the event of a fault on the RS-485 bus.

    Max
  • 0 in reply to Miguel Robertson
    Guru 16770 points

    Hi Max

    Thank you for your reply.

    Let me ask you one more question.

    In datasheet, maximum Vod is not characterized with RL.

    What can we take as maximum Vod?

    I drew yellow line over black line on Figure 16.

    What does this line mean?

    BestRegards

  • 0 in reply to na na78
    TI__Guru 62910 points
    Hello,

    The black line shows the performance of the device - i.e., its VOD for different IO levels. Each point along this curve could be translated into a load resistance by taking VOD/IO. The dashed lines show the V/I relationship for different common resistance values, and their points of intersection with the solid black line indicate the data points on the performance curve corresponding to those resistance values. For example, one intersection point indicates that with a 60-Ohm load the device will source 35 mA and generate 2.1 V. (2.1 V = 0.035 A * 60 Ohms.)

    Max
  • 0 in reply to Miguel Robertson
    Guru 16770 points
    Hi Max

    Thank you for your reply.
    I understand the meaning of Figure 16.

    The customer wants to have maximum vod but it is on datasheet.
    So is it OK to take 35mA as maximum with 60-ohm?

    BestRegards
  • 0 in reply to na na78
    TI__Guru 62910 points
    No, the data in Figure 16 shows the operation of a typical device under nominal conditions and doesn't account for variation from unit to unit or across operating conditions like temperature or voltage. I reviewed our characterization data for this parameter, though, and would recommend using 45 mA as a maximum output current (assuming 60-Ohm loading) in your analysis.

    Regards,
    Max