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LP2981A: Higher Voltage LP2981A

Jean Beauve
Prodigy 90 points
Part Number: LP2981A
Other Parts Discussed in Thread: LP2982, LM4040

Hello,

Is it possible to use a LP2981-33DBVR with a LM4040BIM3X-3.0/NOPB to output 6V3 regulated ?

If it is possible to to so, is it also possible with a LP2982 without the Bypass capacitor ?

Thank you for your answers.

Jean

  • 0
    Prodigy 90 points

    Hello,

    The ideal for me would be to use LP2982-33 and LM4040-33 as per the following schematic.

    What do you think ?

    Thank you,

    Jean

  • 0
    Prodigy 90 points

    Hello,

    At least would it be possible to use the following schematic:

    LP2980-33 has a minimal Ground current of 65µA @ IL of 0mA (in my application IL is about 20mA (Ground current will be around 200µA)

    LM4040-33 needs a IR >= 65µA

    So I don't see why this would not work.

    What do you think ?

    Thank you

    Jean

  • 0 in reply to Jean Beauve
    TI__Mastermind 48995 points

    Hi Jean,

    I have begun looking into your question and will provide a response tomorrow (7/14/20).

    Best regards,

    Nick

  • 0
    TI__Mastermind 48995 points

    Hi Jean,

    After reviewing the datasheets I did not find anything that would suggest that this won't work. My only concern would have been the minimum current requirement, but since the load you will be driving is about 20mA I do not think this will be an issue. However, I must point out that I have not seen the LM4040 used like this and we don't have a simulation model to use, so I cannot tell you with full confidence that this will work. 

    Something else I would like to point out is that the Cout is pretty large in your schematic. In general this is fine, but when the device starts up you may see a very large inrush current, which can have the potential to damage the bonding wire contacts of the LDO. The peak inrush current also depends on the maximum current your unregulated supply can drive, so the severity will depend on your specific application. 

    As for using the LP2982 without a bypass capacitor. The bypass capacitor forms a low-pass filter for the bandgap reference. The LDO will still function, but you will have to contend with more noise at the output. 

    Best regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 90 points

    Thank you Nick.

    As for the output capacitor, you are right, I changed my mind and decreased the capacitor to 10µF.

    Best regards,

    Jean

  • 0 in reply to Jean Beauve
    Prodigy 90 points

    Hello Nick,

    I have build it, but it doesn't work

    Then, I have found some models from workbench and simulated the circuit in TINA with the LM4040-3 model and the LP2985-3.3, It doesn't work 

    I also simulated in TINA a Zener and the LP2985-3.3, it doesn't work.

    It looks like the LP298x familly needs to be tied to ground and not to a virtual ground like a zener or a LM4040, too bad !

    Best regards,

    Jean

  • 0 in reply to Jean Beauve
    TI__Mastermind 48995 points

    Hi Jean,

    That is interesting.

    When you built the circuit, did it not work at all or was the LDO unstable or something like that? Did you probe the GND pin voltage to see if it was actually close to 3V?

    Best regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 90 points

    Hello Nick,

    The GND Pin was around 1V5

    Looking at the LP2980 ADJ, it looks like, the internal band gap is a possible reason why the trick is not working.

    There is something that goes wrong when GND is something else (Sink/Source current ???).

    Best regards,

    Jean