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LP38690-ADJ: Reference voltage is 1.8V instead of 1.25V

Ahmed Mostafa1
Prodigy 20 points
Part Number: LP38690-ADJ

Hi , I'm using this part LP38690SDX-ADJ, with a 6.3V in and 5V out. My top feedback resistor is 30.9k, and bottom feedback resistor is 10k. I'm using a 4.7uF input and output ceramic cap.

Upon measuring the output, it measures at 6.3V, which is the input voltage. When i measured the adj pin voltage, it measures 1.8V. Why is the adjust pin measuring 1.8V instead of 1.25V? I tried 2 different components, both have the same performance.

Is it possible that during the soldering process I applied too high of a temperature, and that affected the setting of the bandgap reference? It seems strange if that were the case, given that on both times the reference measured 1.8V even though I used 2 different temperatures during soldering.

Does it have to the with the ESR of the output cap?

Ahmed

  • 0
    TI__Mastermind 44370 points

    Hi Ahmed,

    If the Adj pin voltage is measuring 1.8V, I suspect that there is a leakage path from VIN to VOUT which is pulling up VOUT. A standard silicon bandgap reference should be ~1.25V.

    Can you check for a short or leakage path from VIN to VOUT?