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LM2576: Why does LM2576-5.0 output 5.4V?

Cristian Monea
Expert 1795 points
Part Number: LM2576

Hello! I'm using LM2576-5.0  DC-DC converter in two designs. In design 1 it works fine, providing 5V, but in design 2 it provides 5V without load, and 5.4V with load (exceeding even datasheet specification). The current consumption is 0.2-0.4A and the voltage input is 12V. If it's helpful, I mention that design 2 is used to power a Raspberry Pi 3 B+, whereas design 1 is used to power a custom PCB.

Design 1

Design 2

As you can see, the design are similar, so one should not expect differences in the voltage output. These are the parts I've used:

Design 1

C3 - EEVFK1K101Q

C7 - 0.1uF

U1 - LM2576T-5.0/NOPB

D1 - MBR360RLG

L2 - PE-92108KNL

C14 - EEEFK1E102AQ

Design 2

C1 - ECA-1JM101

C3 - 0.1uF

U1 - LM2576T-5.0/NOPB

D1 - MBR360RLG

L2 - PE-92108KNL

C4 - 16ZLH1000MEFC8X20

Does anybody have an idea why the voltage output is different in the two designs? And why it is increased only when load is present?

Thank you!

  • 0
    TI__Expert 4100 points
    Hello Cristian,
    From schematic viewpoint, there is no obvious reason for observed behavior.
    To help with troubleshooting please check below:
    1. are all components in design 2 properly soldered. Please check all solder joints and component connections. Pay attention to the ground pad on the IC. If not properly soldered it may cause unexpected behavior.
    2. Are layouts on both designs same?
    2. Please provide switch node, output and inductor waveform for design 2. Capture these signals when not loaded and with expected load. This may help with trouble shooting.


    Regards
    Brani
  • 0 in reply to Brani Dubocanin
    Expert 1795 points

    Hi! It seems that it was a problem with the multimeter. I measured the output voltage with another meter and it showed 5V, as expected. Thank you for the advices.