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TPS7A4101: Input capacitance value

Oba
Genius 16345 points
Part Number: TPS7A4101

Hello,

 

My customer has an question for TPS7A4101.
The datasheet recommends to use 10uF capacitance for input.

In the customer’s system, there is a 100uF capacitance in front of the TPS7A4101 input capacitance(Cin) because they use a half-wave rectifier circuit.
Then they are asking whether they can reduce the input capacitance value from 10uF to 0.1uF.
Is it OK?

 

Regards,

Oba

  • 0
    TI__Mastermind 23361 points

    Hi Oba, 

    I would consider the 100uF capacitor to be "remote", and the TPS7A41 does require a "local" input capacitor of 1uF or higher that could affect the stability. I would suggest following the datasheet recommendation and use a 1uF instead of 0.1uF as local input capacitor. 

    Regards, 
    Jason

  • 0 in reply to Jason Song
    TI__Genius 16345 points

    Hello Jason,

    Thanks for your reply.
    What does "remote" mean in this case? Is it distance between 100uF and IN pin of TPS7A41?

    Regards,
    Oba

  • 0 in reply to Oba
    TI__Mastermind 23361 points

    Hi Oba, 

    Yes, you may consider the input capacitor as a decoupling capacitor which needs to as close to the input pin of the LDO as possible. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    TI__Genius 16345 points

    Hello  Jason,

    Even if 100uF is put closely to VIN pin, do you recommend to use 1uF instead of 0.1uF?

    Regards,
    Oba 

  • 0 in reply to Oba
    TI__Mastermind 23361 points

    If the 100uf is put closely to the VIN Pin, you could use 0.1F.

  • 0 in reply to Jason Song
    TI__Genius 16345 points

    Hello Jason,

    Thanks. Let me confirm one thing.

    >I would suggest following the datasheet recommendation and use a 1uF instead of 0.1uF as local input capacitor. 

    You answered 1uF as datasheet recommendation. But the datasheet highly recommend to use 10uF although 1uF can be used.
    Do you thing 1uF is enough in this case because there is 100uF already?

    The TPS7A4101 high voltage linear regulator achieves stability with a minimum output capacitance of 4.7 μF and
    input capacitance of 1 μF; however, TI highly recommends using 10-μF output and input capacitors to maximize
    AC performance.

    Regards,
    Oba

  • 0 in reply to Oba
    TI__Mastermind 23361 points

    Hi Oba, 

    If the 100uF is very close to the input pin, it can be considered as input capacitors, and adding a 0.1uF or 10uF can help further reduce the source impedance at a higher frequency and potentially improve the AC performance as the datasheet stated. But since you already have the 100uF, they become optional. If space and cost allow, it's recommended to have the additional 0.1uF or 1uF. 

    Regards, 
    Jason