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LM1085: LM1085 Output

TI-CSC
Genius 11725 points
Part Number: LM1085

Hello E2E Experts,

Good day.

I want to 3.85V output. I adjust the resistors according to the formula in the datasheet but I got 4.18V output. Attached is the schematic.

I will feed the gsm module with this regulator I need 3.8-3.95V and 3A regulator. You can advise me of a regulator if you don't find a problem with this schematic.

I also tried swapping new components and the output is the same.

Thank you in advance for your help.

Regards,

CSC

  • 0
    TI__Expert 3830 points

    Hey CSC, 

    It looks like the adjust pin current is contributing a significant amount to the output voltage.

    Using the equation in Figure 13 of the datasheet:

    And assuming the adjust pin current is the typical value in section 6.5 of the datasheet: 

    Your Vout would be a little higher than expected using the resistors you selected.

    In section 7.4.1 of the datasheet we recommend using a smaller R1 to reduce the impact of the adjust pin current on the output voltage.

    If you were to use equation in figure 13 and select R1=121, then R2=251 should be closer to your Vout=3.85V.

    I hope this helps!

    Thanks,

    -Jimmy