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TPS785-Q1: How to choose the output feedback resistor of TPS785-Q1

Part Number: TPS785-Q1

Hi team.

As shown in the figure below, the description in the red box makes the current flowing through R1 and R2 at least 100 times greater than the IFB current listed in the electrical characteristics table.  What is the theoretical basis for this greater than 100 times?  There is also how to consider the influence of FB pin current error term, and obtain the best accuracy?  (According to the manual LDO output accuracy typical value: 0.5%, maximum value: 1.7%).

Is there a specific data book that describes the LDO output feedback resistance calculation method?  Please send me the link.  thank you.

  • Hello,

    Thank you for your questions.

    Please allow me 2-3 business days to answer your questions.

    Thank you,

    Hannah

  • Hello,

    We recommend R2 to be equal or smaller than 550kohm due to optimizing PSRR and noise reduction. IFB is extremely small, typically 10nA, due to it being internally connected to the LDO, through a FET. The current flowing through R1 and R2 should be 100 times greater, because the current IFB is extremely small. If the current flowing through R1 and R2 were to be small as well, then PSRR and noise reduction would not have the ability to be optimized. 

    The LDO group does not have a specific paper on the feedback resistor network, but please look at Design considerations for a resistive feedback divider in a DC/DC converter for guidance on designing with the resistive feedback divider.