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DAC81416: Current on each of the outputs of the DAC

laurent lefevre
Prodigy 120 points
Part Number: DAC81416
Other Parts Discussed in Thread: DAC8775

Hi,

I would like to use the DAC81416 but before can you confirm me that each output can deliver +/-25mA at the same time and in full scale?


For example: OUT0 to OUT15 at 40V on 1.6k = 25mA for each output. That makes a total of 16 x 25mA = 400mA provided by the DAC.


If it is true, is this current supplied by the Vcc power supply?

Regards,
Laurent Lefevre.

  • 0
    TI__Genius 14220 points

    Hi Laurent,

    Welcome to E2E and thank you for your query. You're right that the DAC81416 can deliver 25mA simultaneously from all 16 channels. The limitation is not with the current output but with the power dissipation. Power dissipation across the DAC depends on both current and the voltage drop. For example, you need to provide 3V of headroom from VCC. So, the total power dissipation will be 3V*25mA*16 = 1.2W. You need to add the power dissipated due to the quiescent currents, to this number. 

    This much of wattage cannot be dissipated from a small package without proper heatsinking. Please go through the thermal resistance details to calculate the temperature rise in the junction and design a heatsink accordingly.

    Note that the maximum power dissipation will happen when you move away from the full-scale output. This will increase your voltage drop across the device.

    Hope that answers your question. 

    Regards,

    Uttam Sahu

    Applications Engineer, Precision DAC

  • 0 in reply to Uttam Sahu
    Prodigy 120 points

    Hi Uttam,

    Thank you for your response.

    With the evaluation module DAC81416EVM do you know the maximum power dissipation?

    For my test, I would like to use 12 outputs at 29V and 25mA with a VCC= 32V. Do you think this module is ok for that?

    Regards,
    Laurent.

  • 0 in reply to Uttam Sahu
    Prodigy 120 points

    Hi Uttam,

    I read again your response and I afraid to understand that the headroom voltage is the difference between VCC and Vout. If it is true, the problem doesn't appear when the Vout is near to the full-scale but when the Vout moves away from the full-scale.


    So for VCC=32V and Vout=5V then the headroom is 32-5=27V and the power dissipation for 12 outputs at 25mA will be  12x27x25mA = 8,1W.

    Do I understand well?

    Regards,
    Laurent Lefevre.

  • 0 in reply to laurent lefevre
    TI__Guru 53633 points

    Hi Laurent,

    You are correct in your understanding, drawing more current at a lower VOUT with high VDD supplies is the worst case.

    For your reference, you can look at a device like the DAC8775.  On this device we use some switching power supplies to make the DAC supplies just high enough to drive the output, meaning that there is less power consumption in the part.  I am not necessarily recommending this a replacement for the DAC81416, but just for example.