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LM2682: -6.6V Output?

Filipe Rubinstein
Intellectual 821 points
Part Number: LM2682

Hi all, 

I am investigating using the LM2682 for a 3.3V--> -6.6V application. I attempting to test the device using the following circuit below, but I am receiving an output of  -3.7V instead. If possible, could you verify that this setup is accurate? One thing of note is that I am using ceramic capacitors in this setup, so I am unsure whether this has an impact on device performance.

Thank you.

  • 0
    TI__Guru 61695 points

    Hello Filipe,

    The problem in your setup is that you are using different capacitors on C1+/- and C2+/-. The charge pump charges both to VIN and then puts them in series to discharge them into VOUT. As you are using different values, the discharge happens according a capacitive divider, So an output voltage of -3.7V follows exactly your setup.

    Please equal the 2 caps and then you will get almost -6.6V.

    I am saying almost because there is some loss inside the device on the switches as they have series resistance.

    Best regards,
    Brigitte