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LM1084: LDO outputing ~10V when it's supposed to output 5V

Anthony Gamerman
Prodigy 10 points
Part Number: LM1084

Hello TI forums!

First time posting on here. Some background information on my issue, for a project I ordered a LM1084 5V 5A LDO and followed Texas Instruments datasheet typical application as I found here. I needed a fixed 5V output and so i selected a 120 Ohm resistor for R1 and a 360 Ohm resistor for R2 (in regards to the typical application diagram) and 0.1 uF capacitors for C1 and the tantalum capacitor. 

So moving on from the background information, I fed 12V to the input of the LDO and got ~10V on the output with no load, under a fairly small load there was a slight voltage drop but nothing significant. I ordered the part off of Digikey from this link as well. Ive tested every passive component in the circuit and they all read their expected and determined values. I cant figure out what might be wrong with the LM1084, could i have gotten a bad batch from TI or Digikey? The text on the part itself from Digikey indicates that it is the correct part however its outputting ~2 times the voltage than expected. Anyone have any ideas, suggestions or troubleshooting ideas?

Thanks, Anthony Gamerman

  • 0
    TI__Guru 55940 points
    Hi Anthony,

    Thanks for trying out the forums! From your description there is nothing obvious as to why your output is not at 5 V. In order for me to help debug remotely, could you provide a multi-channel scopeshot of Vin, Vout, Vadj, and Iout? This multi-channel scopeshot will help show the relationship between the rails.

    In addition, one thing that is often overlooked initially in debugging are unintentional leakage paths. Sometimes there are unintentional bias paths in the load that the linear regulator is powering if the load requires multiple input rails. Another common leakage path is leftover flux from soldering that was not properly removed from the PCB board.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Guru 55940 points
    Hi Anthony,

    Since it has been several weeks without a reply, I assume that this thread is resolved. If this is not correct, please feel free to post again.

    Very Respectfully,
    Ryan