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TPS7A47: (TPS7A4701 and TPS7A33 8.192V

mohamed mohamed
Prodigy 50 points
Part Number: TPS7A47
Other Parts Discussed in Thread: TPS7A33

Hello,

any suggestion on the resistor selection to get the most accurate +-  8.192v  from the TPS7A4701 and TPS7A33

Thank you

  • 0
    TI__Guru 55940 points
    Hi,

    This comes down largely to how much board space you and what rating resistors you choose to purchase. The equations for setting the resistor divider are given in each respective datasheet; however, assuming standard 1% resistors it will be difficult to find resistor pairs that will give you your exact desired voltage. One workaround that is used is to split R1 into two resistors R1A and R1B so that R1A + R1B = R1. This allows for a more accurate resistor divider at the cost of extra resistors and board space.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 50 points
    space is not an issue, just accuracy is what I am after, I know the equation, just not wondering if someone did the work to find the most accurate resistors values (avaliable) for the that voltage
  • 0 in reply to mohamed mohamed
    TI__Guru 55940 points
    Hi,

    I am not aware of anyone having calculated your specific voltage rail. Please note that when calculating your system accuracy you will need to account for the resistor accuracy as well. The following application report shows how to factor in the resistor tolerances into your accuracy:

    www.ti.com/.../slva423.pdf

    Very Respectfully,
    Ryan
  • 0 in reply to mohamed mohamed
    TI__Mastermind 22610 points
    Best 0.1% pairs for Vout=8.192V from my worksheet:

    For TPS7A3301 with Vref= –1.175V
    R1 (top) 25.5k +/-0.1%
    R2 (bottom) 4.27k +/-0.1%
    Vout = (-1.175V (1+(25.5k / 4.27k) ) ) = -8.191978V
    (Note : Datasheet formula ignores the small Vout error, 357uV, from the Ifb current through R1)

    For TPS7A4701 with Vref= 1.40V and Iref= 350nA ...
    R1 (top) 11.5k +/-0.1%
    R2 (bottom) 2.37k +/-0.1%
    Vout = (1.40V (1+(11.5k / 2.37k) ) ) + (350nA x 11.5k) = 8.197274V
    Verror= 0.005274V
    %error = 0.064%