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LP2950 Issue

Sridhar Jonnalagadda
Prodigy 240 points
Other Parts Discussed in Thread: LP2950

Hi,

We are using the 3 pin LP2950 3.3V part in our system running from 24V DC supply. The intent is to generate 3.3V and use this to power the logic on the board.

I have used 10uF ceramic cap on the input side and 10uF ceramic cap with 2 Ohm resistor is series on the output side. We are seeing a output of around 5.42V from LP2950 which is unexpected.  Is there anything that you could suggest to debug this behavior? Is the cap selection okay?

Best Regards,

Sridhar

  • 0
    TI__Mastermind 22610 points

    Agreed that 5.42V out is not correct, and with only three terminals on LP2950-3.3 it is difficult to to visualize how there could be any connection errors.

    The output will require some minimum load. The datasheet calls for 100uA minimum (3.3V/100uA = 33 k Ohms).

    The ceramic output capacitor should be X5R/X7R (or better) and the selection should include capacitance value de-rating due to applied DC voltage. The same would apply for the ceramic input capacitor selection.

    The stated output capacitor (10 uF + 2 Ohms) should be adequate, but I do recommend that you check the output pin for oscillation at the minimum and maximum loading.

    I would suggest that the 2 ohms series resistance added to the output capacitor to simulate ESR could be reduced to approximately 0.1 Ohms (100 milli-Ohms). Not required, but the lower ESR resistance should improve the output dynamic behavior.

  • 0 in reply to Donald Jones
    Prodigy 240 points

    Thanks Donald Jones. Appreciate your help. We are able to resolve the issue and move forward.

    Best Regards,

    Sridhar