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Original question:

TPS7A14: Facing issue with TPS7A14EVM-058 EVM

TPS7A14: Design flexibility for Variable output

Nanthan raj
Intellectual 270 points
Part Number: TPS7A14
Other Parts Discussed in Thread: TPS7A13, TPS7A11

Hi,

Currently we are using TPS7A1412PYBKR in our product which gives 1.2V fixed output. We want to adjust the output voltage to get 1.25V but we could not find the replacement part TPS7A14125 in online.

Since our design has feedback resistor placeholder on the TPS7A1412PYBKR circuit we have mounted the R1,R2 values to get 1.25V as per below application note. We didn't get the expected voltage and observed 1.33V instead.

www.ti.com/.../sbva092.pdf

What is the actual VREF voltage & feedback resistor value for TPS7A1412PYBKR to get 1.25V output? 

Regards,

Nanthan.

  • 0
    TI__Mastermind 37005 points

    Hi Nanthan,

    How many TPS7A14 LDO's do you estimate your production will require at 1.25V? If the business case is strong it may be easier for us to create those for you.

    What values of external feedback resistors did you use which generated 1.33V on the output? I noticed that the white paper does not mention the sense pin current.  The summation of the top and bottom setpoint resistor will want to be less than 62.5k in order to swamp out the effects of the sense pin current.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 270 points

    Hi, I do not have the exact production numbers now and estimate would be around 2K-5K. But we need at least 5 samples to test before production. 

    And considering Vref as 0.8V we have used R1-5.6K,R2-10k ohm.

    Regards,

    Nanthan.

  • 0 in reply to Nanthan raj
    TI__Mastermind 37005 points

    Hi Nanthan,

    I think you have the wrong setpoint resistors. The app note used the TPS7A1408 version of the device, which is a 0.8V output. Normally the SNS pin is operating as unity gain feedback but if you adjust it to be a feedback pin, the LDO will act as "Vref" = 0.8.  In your case you are using the TPS7A1412 version, which is an output voltage of 1.2V.  Thus your Vref should be 1.2V not 0.8V.  If you change R1 = 422 ohms, you should see 1.25V on the output.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 270 points

    Hi Stephen,

    Yes, that resolved my issue for 1.25V output. Thanks.

    In similar case we have to increase another power rail voltage to 1.55V from 1.5V which derived from TPS7A1115PDRVT.

    Do you have any suggestion for the replacement part to get 1.55V output ?

    Regards,

    Nanthan.

  • 0 in reply to Nanthan raj
    TI__Mastermind 37005 points

    Hi Nathan,

    Can you use the TPS7A13 (same as the TPS7A14 but the TPS7A13 has a current limit = 500mA, the same as the TPS7A11)?  You would use the same concept to derive the 1.55V with the TPS7A13 as you used with the TPS7A14.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 270 points

    Hi Stephen,

    Thanks for your suggestion. TPS7A13 is not available with DRV package and not possible to replace in our current design . But I hope that we can use TPS7A1412PDRVR to derive 1.55V output by adding feedback resistors.

    Regards,

    Nanthan.

  • +1 in reply to Nanthan raj
    TI__Mastermind 37005 points

    Hi Nanthan,

    Yes, the TPS7A14 option should work too.

    Thanks,

    Stephen