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TPS7A85: R1/R2 setting at Vout =~ 0.8V

Kazuhiko Hirano
Genius 15078 points
Part Number: TPS7A85

Hellow,

 

TPS7A85 datasheet states as follows.

 

“R1 and R2 can be calculated for any output voltage range using Equation 8. This resistive network must provide a current equal to or greater than 5 μA for dc accuracy. Using an R1 of 12.1 kΩ is recommended to optimize the noise and PSRR.”

 

But to get near 0.8V Vout, keeping R1 = 12.1 kΩ is difficult.

For example, if you want exact 0.8V Vout, if R1 = 12.1 kΩ, R2 gets infinite.

To keep R2 as finite value, R1 gets zero << 12.1kΩ. Is this not good from noise and PSRR point of view?

 

To get 0.8V Vout, what values should R1 and R2 be respectively?

 

Best regards,

 

K.Hirano

  • 0
    TI__Guru 55940 points

    Hi K.Hirano,

    While we recommend using a top resistor (R1) of 12 k for most applications, it is okay to use other resistors.  For a 0.8 V output, you can simply short FB to OUT.

    Please also consider our newer generation TPS7A85A.  This LDO is pin-to-pin compatible with TPS7A85 but offers some additional flexibility in that there is no sequencing requirement for IN, EN, and BIAS.

    Very Respectfully,

    Ryan