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Nick Gray

 

Nicholas Gray

Nicholas has worked in the Semiconductor industry for over 30 years and has authored a number of published articles about data converters (ADCs and DACs) and signal integrity issues.

 

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  • Dear sir,

    I want to use AD5428 in my circuit,how can i calculate  the power consumption of a current-DAC  ?

     

    thanks

  • in reply to Former Member
    There are three components to the power consumption of the AD5428: latches and driver power, R-2R ladder power and feedback resistor power. It turns out that power consumption in the R-2R ladder and power in the feedback resistor are the same.

    The “Power Requirements” specification on page 4 of the data sheet indicates the power consumption of the switches and latches. The maximum power consumption would be when the die is hot, so we look at maximum current consumption over the operating temperature range and find it to be 10 microamps (uA) at 5.5V, so this component of maximum power is 55uW.

     

    The reference sees an impedance of “R” in the R-2R ladder, so the power in the ladder is the square of the reference voltage divided by “R”, which can be between 8k and 12k Ohms, per page 16 of the data sheet. Maximum power consumption will be with 8k resistors in the ladder and 12k resistors for the feedback resistors. The actual feedback resistor current will depend upon the digital input word to the DAC, but the maximum current in the feedback resistor is the same current flowing in the ladder. The maximum power in the feedback resistor will occur when the feedback resistor is at its maximum, or 12k. But the feedback and ladder resistances are the same.

    The bottom line is that maximum power consumption is maximum when the ladder and feedback resistor are minimum and the total power there is 20.5mW. Add to this the 55uW consumed in the switches and latches and we have 20.555mW maximum power consumption of the device.

    Again, keep in mind that the output current will depend upon the DAC input code. The result is that, at an input code of zero, maximum power consumption will be 12.555mW.

    I do hope that this is the information you are seeking.

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  • in reply to Former Member
    There are three components to the power consumption of the AD5428: latches and driver power, R-2R ladder power and feedback resistor power. It turns out that power consumption in the R-2R ladder and power in the feedback resistor are the same.

    The “Power Requirements” specification on page 4 of the data sheet indicates the power consumption of the switches and latches. The maximum power consumption would be when the die is hot, so we look at maximum current consumption over the operating temperature range and find it to be 10 microamps (uA) at 5.5V, so this component of maximum power is 55uW.

     

    The reference sees an impedance of “R” in the R-2R ladder, so the power in the ladder is the square of the reference voltage divided by “R”, which can be between 8k and 12k Ohms, per page 16 of the data sheet. Maximum power consumption will be with 8k resistors in the ladder and 12k resistors for the feedback resistors. The actual feedback resistor current will depend upon the digital input word to the DAC, but the maximum current in the feedback resistor is the same current flowing in the ladder. The maximum power in the feedback resistor will occur when the feedback resistor is at its maximum, or 12k. But the feedback and ladder resistances are the same.

    The bottom line is that maximum power consumption is maximum when the ladder and feedback resistor are minimum and the total power there is 20.5mW. Add to this the 55uW consumed in the switches and latches and we have 20.555mW maximum power consumption of the device.

    Again, keep in mind that the output current will depend upon the DAC input code. The result is that, at an input code of zero, maximum power consumption will be 12.555mW.

    I do hope that this is the information you are seeking.

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