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LDO parameters in Datasheet

Alexander Ozerov
Prodigy 30 points
Other Parts Discussed in Thread: TLV759P, LM2990

Hi!

Can You explain definition some LDO parameters in datasheets? My ask about line and load regulation. Document SLVA079 (http://www.ti.com/lit/an/slva079/slva079.pdf) define description for line and load regulation. It is ratio of delta Vout to delta Vin (Iout). But in some datasheet parameters indicated in Volts (LM2990,  in example), volts and V/A (TLV759P). How i can properly measure this parameters in my design and how i must understand parameters in datasheets? Can you recommend some standards for measure this parameters?

  • 0
    TI__Mastermind 23361 points

    Hi Alexander,

    This is a very good question. As we can see, LM2990 was developed in 1999 or earlier, and TLV759 was developed in 2018. For older devices like LM2990, the line, and load regulation are normally defined with a min and max at the full line or load conditions. The TLV759P, however, has the definition of the load regulation using V/A as for some customers, they are not using the full load, and having V/A will give better typical numbers for their application. 

    For the measurements, which parameters do you plan to measure? 

    Regards, 

    Jason Song

  • 0 in reply to Jason Song
    Prodigy 30 points

    Thanks, Jason!

    I thought about older and new devices and various methods for parameter measurement. Define V/A parameter is really better for customer. This will help more precisely modeling real device. 

    I create LDO Automate test system prototype for my students project. Line regulation and Load regulation is one from parameter set. I find some discrepancy in related documents for line and load regulation definition. I would like to find standards for LDO parameters measurement requirements and technique. This standard must help me create unification set of parameter set for all LDOs and make right measurements.

    Best regards,

    Alexander

  • 0 in reply to Alexander Ozerov
    TI__Mastermind 23361 points

    Hi Alexander, 

    Here in the lab, we are using source measurement units (SMU) for line and load regulation measurements.

    For line regulation, automated testing should force a Vin voltage at min and max range of the supply and measure the output with another SMU. The SMU at the output will force 1mA of current when taking the output voltage. The line regulation is defined on how the output would change within the whole working range of the Vin. 

    For load regulation, depending on how much the load is, for large current, we normally have an SMU in current mode between the output and the input and having another one at the same time to provide Vin. The reason for us to have the SMU between the output and the input is to have the load current directly feeding back to the input. When taking the reading on the output, please allow a few milliseconds for the output to settle, and the setting is normally called source delay. It's also good practice to take hundreds of readings and to output the averaged one. This also applies to the line regulation measurement. The load regulation is defined as the output change across the full load. 

    When taking the load regulation, use the thermal equation to calculate the junction temperature to make sure it's not violating the recommended junction temperature max. Here in the lab, for some high power LDO, we have to use pulsed current load to not overheat the LDO. 

    Hope this helps, if you have any additional questions, please do not hesitate to let me know. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 30 points

    Hi Jason!

    Big thanks for explanation!

    I create SMU-based system. This system can measure LDO parameters within the whole range of inpit and output condition. 

    Special thanks to use pulsed current for high power LDO!