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TPS7A85A: Clarification needed in description (Section 8.1.1.1 Adjustable operation)

Karteek Sreedharala
Prodigy 20 points
Part Number: TPS7A85A


I am interested in this IC (tps7a85a). In section 8.1.1.1 it is mentioned that "R1 and R2 can be calculated for any output voltage range using . This resistive network must provide a current equal to or greater than 5 μA for dc accuracy. TI recommends using an R1 approximately 12 kΩ to optimize the noise and PSRR."

Is it mandatory to have R1 to be around 12.1Kohms? Can I use some other value (say 1K-6K) as long as I maintain resistive current equal to or greater than 5uA?

Example: to achieve 0.9V in adjustable mode, I would like to use R1=5K and R2=40K. Is this fine? 

  • 0
    TI__Genius 14245 points

    Hi Karteek,

    You can certainly use other R1 values. The noise and PSRR are optimized for 12kΩ however, the difference in performance will be very small. 

    Also since your target Vout is less than 3.95V you could use the ANY-OUT feature to set the output voltage without needing any external resistors. This would increase the overall accuracy of the design (since the resistor tolerances would be accounted for) and would be optimized for noise and PSRR. For your application  you would just need to ground the 100mV pin to get 0.9V on the output. 

    -Kyle

  • 0 in reply to Kyle Van Renterghem
    Prodigy 20 points

    Hi Kyle,

    Thanks for the reply !!

    I want to control the output voltage using a pot or ADC. Hence prefer adjustable option using feedback resistors.

    Regards,

    Karteek.S