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LM4050QML-SP: Power supply to multiple ADC128S102QML and DAC121S101WGRQV

Danilo A.
Mastermind 24735 points
Part Number: LM4050QML-SP
Other Parts Discussed in Thread: DAC121S101QML-SP, ADC128S102

Hi Team,

Figure 14 of the datasheet of LM4050QML and Figure 43 of DAC121S101WGRQV show that it can be used as power supply and reference to ADC128S102QML and DAC121S101WGRQV. Our customer would like to know how many ADCs or DACs can be placed on one LM4050-5.0QML. There are ten DAC121S101WGRQV and three ADC128S102WGRQV in their application. 

Regards,

Danilo

  • 0
    TI__Expert 7185 points

    Hi Danilo,

    The LM4050QML-SP can be used as a power supply as long as the current through the device is above the minimum operating current and below the maximum operating current. For the 5V version of this part, this is 74uA to 15mA.

    There are equations below the datasheet Figures that describe what the minimum and maximum values are for the resistor placed between the supply voltage and the LM4050QML-SP. From an operating current standpoint, the number of DACs and ADCs the LM4050QML-SP can support will depend on the variables in those equations: 

    R_min = ( Vsupply_max − Vout_min) / (IA_min + IR_max)

    R_max = ( Vsupply_min − Vout_max) / (IA_max + IR_min)

    where

    • Vout_min and Vout_max are the nominal LM4050QML-SP output voltages ± the output tolerance over temperature

    • IR_max is the maximum allowable current through the LM4050QML-SP (15mA)

    • IR_min is the minimum current required by the LM4050QML-SP for proper regulation (74uA)

    • IA_max is the maximum combined DAC and ADC supply current

    • IA_min is the minimum combined DAC and ADC supply current

    As long as it is possible to select a resistor that is between R_min and R_max, the operating current conditions for the LM4050QML-SP can be met. The customer will need to plug the values for their design into these equations.

    Thanks,

    Sarah

  • 0
    TI__Expert 7185 points

    Does the customer only plan to use the LM4050QML-SP as a power supply, or do they also want to use it as a reference? There may be additional considerations for the DACs and ADCs if they want to use the LM4050QML-SP as a shared reference.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 60 points

    To Sarah,

    DAC121S101QML-SP: The supply voltage for the DAC121S101QML-SP serves as its voltage reference per TI datasheet page 1.

    ADC128S102QML: Positive analog supply pin. This voltage is also used as the reference voltage per TI datasheet page 4.

    Regards,

    F. Dennis Streetman

  • 0 in reply to F. Dennis Streetman
    TI__Expert 7185 points

    Thank you for confirming. This configuration is acceptable. 

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    TI__Mastermind 24940 points

    Hello Team,

    Regarding the ADC128S102. as noted, the analog power supply is the reference for the ADC128S102, thus any noise or movement on the power supply will be directly reflected in the ADC measurement. At 12 bits, this may not be an issue for the customer.

     I would like to know if the three ADC128S102 devices will operate simultaneously. This will likely encounter issues if this is the case. The current consumption for the device will experience transients during conversions that can jump up to the milliamps range.  Thus if the 3 devices are converting at the same time, it  will likely demand more than 15mA, the max for the LM4050QML-SP. If this is the case, I would suggest staggering when the ADCs are actively completing conversions.  

    Other than this, this looks fine as far as the ADC128S102

    Regards

    Cynthia