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LM5013-Q1: Vfb drops below 1.2V

Grad Tacken
Prodigy 101 points
Part Number: LM5013-Q1
Other Parts Discussed in Thread: LM5013

If I use the LM5013 with light loads <50mA the output has a large ripple of 3Vpp. If I measure Vfb I would expect this to be around 1.2V but it going as low as 1V before it turns on the output fet see picture below.  How can this happen and how to solve this?

Application 12V out

Input 12.3 - 15V

Load 15mA - 500mA

Yellow is output voltage
Green is FB pin.

  • 0
    TI__Mastermind 31315 points

    Hi Grad,

    Looks like you are seeing the IC enter sleep mode behavior. This happens when you are operating at very light load and basically the IC will only turn on once the voltage on the feedback pin drops below a certain value. 

    In order to not have light-load switching, you can try to 1) add a dummy load to the output or 2) pick a different IC with forced PWM (FPWM) operation. 

    Regards,

    Richard