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ADP3331 problem

Hi,

I tried to use ADP3331 to get a low noise 4V power supply. Whatever I do I can't get a stable output. I used 392k and 909k resistors as a voltage divider and sometimes I managed to get stable 4.2V (in two different PCBs), but usually I get a very low output voltage (like 1.5-2.0V) that rises very very slowly (over a minute) and sometimes reaches 4V, sometimes something like 3.6V.

I tried to put different capacitors (1u, 10u, etc.) with different dielectrics (X5R, X7R, tantalum) very close to the input and output pins, but that didn't help. Input voltage is 6.0-6.5V.

I never had such strange problems with other regulators (although I used only fixed-voltage low-dropout ones and adjustable non-low-dropout).

Do you have any suggestions?

Best regards,

Piotr

  • I have the same simple schematic, as on the first page of the datasheet. I tried to connect resistors (50, 100 ohm) as a load. I use a bench power supply. I tried with and without noise reduction elements (100k, 1n). On the scope there are no oscillations, just a steady rise of the voltage.

    Best regards,

    Piotr

  • Piotr,

    can you share your schematics with us? Are you using any of the noise reduction fucntions or are you using it as a controller with external pass element or anything else we need to know?

    What load is connected to the output of the LDO?

    What do you use to power this LDO (a bench supply, a battery or some other power source?)

    Can you measure with the scope the input voltage and the output voltage during this power-up transition?

    LucaV

  • I have never see this problem, my suspicion is that something is not connected right (GND pin maybe) or the power connection traces.

    it would be good to measure the voltage at every pin when the Vout is not what you expect it to be.

    LucaV

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