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TPS7B4250-Q1: Consult to experts form TI,the operating principle of tracking LDO,such as TPS7B4250-Q1,thanks for you.

Hello Kitty
Prodigy 190 points
Part Number: TPS7B4250-Q1

Dears

Do you know the operating principle of tracking LDO,such as TPS7B4250-Q1.Could you help to describe the details of it?

How do ti works?

Thanks for you.

  • 0
    TI__Mastermind 23361 points
    There is an application note that explains various applications with tracking LDO, you can find it here.
    www.ti.com/.../slva789.pdf

    Let me know if it meets your needs.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Prodigy 190 points
    Thank you,I have read the document,it explained the applications of tracking LDO,but didn't explain the operating principle of tracking LDO.
  • 0 in reply to Hello Kitty
    TI__Mastermind 23361 points

    For the operating of TPS7B4250-Q1, there are three things that are different than regular LDOs. 

    1. An external reference needs to be provided in a range of 1.5V to 18V. 

    2. The output's tracking feature allows it to follow the external voltage rail or reference. 

    3. The device will start operating once Vin is higher than Vuvlo(Minimum Vin = 4V). The tracking will start once the external reference voltage exceeds 1.5V. A negative falling edge lower than 0.8V will turn the device into inactive mode which will provide reduced quiescent current. 

    Please let me know if this answers your questions. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 190 points
    Thanks and sorry,I want to know the principle.
    For Example,why does the tracking LDO could track the external reference voltage,but regular LDO couldnot track the internal reference voltage?
    Is there any difference external reference and internal reference?
    Why does the tracking LDO could reduce the dropout of long cable and regular couldnot?
    Best regards for you
  • 0 in reply to Hello Kitty
    TI__Mastermind 23361 points

    1. I talked to a designer and according to him, usually the tracking LDO is dynamically changing its internal voltage reference set by the external reference, that's when Vout is tracking Vref. Once it reaches the desired Vout, the reference might be switched to its internal reference, such as bandgap voltage; the loop gain may also get changed during the switching. There would be different approaches to implement the concept in the circuit, if you are interested, you may need to find some textbook or application notes on this topic to explore more. 

    2. I am not sure if I understand your second question on "Why does the tracking LDO could reduce the dropout of long cable and regular couldnot?" Long cable is usually discussed in the applications that in the car system, the main circuit board needs to power on some sensors through long cable and transmitting power. In this kind of application, tracking LDO serves as a protection to the main board from the potential short-to-ground or short-to-battery situation resulted in the long cables. Let me know if this answered your questions. 

    Regads 
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 190 points
    So grateful for your answer,you have answered my questions well.