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LM2611EVAL: Output Current

Matthew Anauo
Prodigy 140 points
Part Number: LM2611EVAL
Other Parts Discussed in Thread: LM2611,

I am trying to use the LM2611EVAL to demonstrate a 3.3V to -12V regulation setup. The load current requirement is 150mA. From the figures and calculations in the datasheet, this should be within the abilities of the LM2611, however using the eval board the output voltage crashes once the load exceeds ~90mA. Nothing on the eval board is changed except the feedback resistors, and I am getting the correct output voltage up to to the point where the output crashes. Is this design beyond the limitations of the LM2611?

  • +1
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. Which values did you use for the FB divider? It might be that the device is entering current limit, if you increase a bit the VIN (for example to 4.5V) do you have  a higher load current capability? 

    Kind regards,

    EM

  • 0 in reply to EM
    Prodigy 140 points

    Hello,

    My feedback divider values are 44.2k (upper) and 5.0k (lower).

    Increasing VIN does indeed increase the load current capability. For my understanding can you clarify what exactly is being current-limited? The worst-case switch current from the 3.3V input should be only about 520mA, and the datasheet specifies the minimum switch current as 0.7A? This did solve my problem but I'd like to fully understand before I include in the design.

    Thanks.

  • 0 in reply to Matthew Anauo
    TI__Genius 11215 points

    Hello, 

    Thanks for your feedback. At which VIN are you able to get the desired load current? Can you share the scope plots of the Vout and SW node? This problem might be caused because you are close to the Max duty cycle (min value in the datasheet). If you try to regulate to a lower Vout (in absolute value, to have a lower duty cycle) what happens? 

    Kind regards, 

    EM