This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • TI Thinks Resolved

DAC7718: the device is heating up

Expert 4390 points

Replies: 3

Views: 134

Part Number: DAC7718

Team,

we observe the DAC7718 heating up to 45 degrees C when the negative -5V voltage is applied to AVss (through a 1kOhm resistor). The AVss is taking 2.5mA, its voltage is -2.5V.

When Avss is grounded, the device is not heating up. The AVdd is +15V so within the EC recommendation. 

We need to apply negative voltage since it helped achieving reasonable accuracy of the output voltage.

Is it fine or should it be heating up like this?

Thanks for your help.

TI Customer

  • Hello Bartosz,

    Can you please share a schematic for your design?

    When you make your AVSS current measurement what are the DAC outputs set to and what load are they driving?

    Kevin Duke
    DAC Applications Manager

  • Expert 4390 points

    In reply to Duke of DACs:

    Hi Kevin,

    I've shared with you the schematic offline.

    The outputs are unconnected - there's no load. Status of outputs is as after a reset.

    Kind regards
  • In reply to Bart:

    Hi Bart,

    Page 19 of the datasheet gives a quiescent current figure for AVSS in normal operation at mid-scale code of -2.7mA typical and -4mA maximum. Of course the outputs will consume a bit more current when driving to a non-zero output voltage, but 2.5mA does not seem significantly unreasonable.

    This level of power dissipation alongside the thermal impedance figures in the datasheet do not suggest that this is the root cause of the device heating up - the QFN package thermal impedance is 27.5C/W so it would have to be burning nearly 1.5W for this to add up, meanwhile maximum power dissipation is only 225mW.

    I did notice, though, that the thermal pad looks to be connected to the "GND_IZOA" net which is what I suspect to be the issue. The note on page 11 beneath the QFN drawing indicates that the thermal pad should be connected to the same net as AVSS or left floating. The thermal pad is electrically connected to the substrate of the device, so connecting it to GND will cause additional current flow which is probably the source of heat. This would also explain why the issue goes away when AVSS is instead connected to GND.

    Please see about getting the PCB reworked to either float the thermal pad or connect it to AVSS and see if that resolves the issue.

    Kevin Duke
    DAC Applications Manager

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.