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LP2992: LP2992 output issue

jeno.zhang
Expert 2555 points
Part Number: LP2992

Hi，

The theoretical output of LP2992M5-3.3/NOPB is 3.3V, and individual output of the customer's circuit board is 1.5V. On the schematic diagram, the C15 capacitor was removed and resoldered, and the normal output of 3.3V can be restored. The welding problem has been basically ruled out. Please help analyze the cause. The schematic diagram is shown below：

Thanks！

  • 0
    TI__Mastermind 36185 points

    Hi Jeno,

    This is a common problem with PCB contaminants, usually solder flux, remain on the PCB after soldering or rework has been performed around the BP capacitor.  Internal to the LDO is a large series resistance that, when combined with the BP capacitor, form an RC filter.  If significant leakage exists across the BP capacitor then this will also form a voltage divider on the reference, which will reduce the output voltage accordingly.  A less common issue is a damaged BP capacitor, but this may also have been the reason for the additional leakage (as opposed to solder flux).

    We recommend using water soluable flux and after carefully soldering the BP capacitor to the PCB, using distilled water to wash away any remaining flux residue.  A DI bath usually takes care of the rest of the flux underneath the capacitor.

    Thanks,

    Stephen