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TPS54040: Output Voltage Drop

Part Number: TPS54040

Hi

I am using TPS54040 to transfer voltage from 12V to 3.3V, but somehow the output voltage drop to 1.8V or 0.7V in some of the products after assemble. In the following are my waveforms and PCB layout. Sometimes it became normal when I remove the glue filling of the products and test the PCB, sometimes it not. So I assume it should be some noise that has affect on the pins of IC, could you pls give some advices on this cases and tell me what reasons may cause this? thanks a lot!

CH1:VIN12V) CH2:EN  CH3:VOUT

CH1:PH CH2:COMP CH3:VOUT

CH1: PH CH2:COMP CH3: VOUT CH4:BOOT

Manu

  • Hello Manu,

    Thank you for using our product.  Sorry for the delay because the E2E server was down for a few days for maintenance. 

    From your scope picture it looks like there is no soft start.  With proper soft start, the output voltage should rise up smoothly like in Figure 53 of the datasheet.  Please double check your SS capacitor C34.

    Thanks,

    Youhao

  • Hi Manu,

    Since there is no update for 3 weeks, may I assume the issue is resolved so I can close this thread?  You can re-open it by adding a new post. 

    Thanks,

    Youhao