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Original question:

TPS745-Q1: LDO PSRR Test Measurement

TPS745-Q1: Recommendation value to design the TPS745-Q1

Ihzany Vilia Devi
Prodigy 215 points
Part Number: TPS745-Q1

Hi,

I Would like to know is there any recommendation value for this each component, if there is no recomendation can you give me a calcculation to how to determine the value ? 

Thank you 

 

  • 0
    TI__Expert 3870 points

    Hi Ihzany,

    For the capacitors you can follow the recommended specs table, which as an example give you the minimum and maximum for Cout, as well as a typical value for Cff. 

    For more information on Cff please see this documentation.

    The RPG pull-up resistor can range from 10kΩ to 100kΩ.

    To set R1 and R2 please use the equation below, where VFB = 0.55V. Also, make sure to also use equation 3 in order to verify R1 + R2 are large enough, IFB = 0.01uA typically for this LDO.

    Regards,

    Andres

  • 0 in reply to Andres Sagredo
    Prodigy 215 points

    Hi Andres,

    What about Cin ? is there any calculation so i can know the right value for the Cin?

    Thank you 

  • 0 in reply to Ihzany Vilia Devi
    TI__Expert 3870 points

    Hi Ihzany,

    For Cin there is no calculations since this is not part of the control loop of the LDO. The main purpose for Cin is for impedance matching anything before the input of the LDO. Generally, a larger Cin is used whenever the input line is jittering or to prevent brown outs. On other cases you can get away with a smaller Cin for the LDO. 

    The Cout can be adjusted depending on transient performance expected, this post covers a quick calculation .

    TPS745-Q1 has a transient response time of roughly 750ns for your Cout calculation.

    Regards,

    Andres