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.

LP2992 - LDO operation below its regulation voltage

Other Parts Discussed in Thread: LP2992

1. For the LP2992 device (assuming a 3.3V part), what happens if the input voltage is below 3.3V (but above the Vin minimum, which I believe is 2.2V). Will the Vout follow (track) the Vin, or will the regulator output be off (0V) ?

2. If the LP2992 does not operate in this fashion (ie: output tracks input when Vin <= Vreg), then is there some other LDO which does behave this way ?

  • The output will track the input (with a difference which is the dropout), but not for low voltages less than the minimum dropout and in principle, I don't know if the manufacturer guarantees you the Vout values for low Vin. Why do you need that, what are you trying to check?

  • Vout tracks Vin when Vin is above approx 1V at room temp. LP2992 does not have UVLO circuit, so Vout stops tracking Vin when the control circuitry does not have enough headroom This will vary a bit with temperature due to Vbe tempco.

    The following graph is valid for rising or falling Vin, minimum output load current, and at room temperature...

  • Thanks Donald.

    The graph you posted is not in the current data sheet for the LP2992.

    Do you have any idea what happens if the load current is larger (say 50mA). Will the output track the input with some small voltage drop (like the dropout voltage shown on the data sheet) ?

  • "... The graph you posted is not in the current data sheet for the LP2992..."

    You are correct. Data was collected and the graph created today in response to your question.

    Since this is outside the guaranteed operating range, it's inclusion in the data sheet would be informational only, and not a requirement.

    Yes, once Vout is tracking Vin, the pass element is saturated and the typical Vdo value can be subtracted from the Vout line.

     

  • Thanks Donald, this all sounds encouraging for our (somewhat unusual) application. We will give it a try.