This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

REF3330: Operation in Dropout

Part Number: REF3330


I'm writing to ask about operation of the REF3330 when in dropout.

Specifically here are my conditions:

VIN = 3.3V +/-5%

VOUT = 3.0V

IOUT = 4mA (max)

My questions are such:

1. Is the output voltage stable? Will the device turn off under these conditions?

2. Does the output voltage start to decline when the input voltage declines past the point of dropout?

3. What about noise?    Will input noise ripple through to the output when the device is operating in dropout?

Many thanks in advance!


  • Hi Donald,

    1. For stability I need to see a schematic. The specifications sound good but I need to see what is around the device.
    2. Yes that can happen, especially if more current is needed than what the device can provide.
    3. Depends on the frequency. Check PSRR because it depends on the frequency of the noise.

  • Hi Guys,

    I've attached the portion of our schematic pertaining to the REF3330:  At the TOSA, the 3.0V reference is used to provide the reverse bias voltage needed for our 3 photodiodes.  The max current for the 3 photodiodes combined is ~3.8mA.

    I'll try to run some tests in our lab to see how the output behaves as the input voltage drops.  Any additional input you can provide would be appreciated.


  • Hi Scott,

    The only comment I have is that I do recommend a 1uF - 10uF input bypass cap while in the schematic there is 20.2uF as per section 9.4 of the DS.
    Besides that, it looks good!



    If you feel this is resolved, please selected Answered.

  • Thanks for the feedback.

    I ran a quick test in the lab with an output current of ~4mA and the input voltage ramping down.  The output looks to be well behaved with no signs of instability under these conditions which is our main concern.

    Thanks guys.