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LM3488Q-Q1: LM3488Q-Q1

German Shevchuk
Prodigy 10 points
Part Number: LM3488Q-Q1
Other Parts Discussed in Thread: LM3488, LM5155, LM5121

 Hello support team,

I use LM3488 for conversion - from 12v  to 24v.

(classical boost converter)

it should support up to 2.2A at the output (short pulse), for some worst case, but the planned average current consumption will not exceed 2A.

I tried practically the schematic , suggested by TI's tool WeBench, but I encountered in some issue - hard inrush current, at the beginning of the operation , which reaches 5A !

there is some "soft-start" feature already implemented in LM3488, I saw delay about 2ms - between rising of 12v at the input and start of DC/DC switching, generally this soft-start feature works, but it is not enough...

could you please suggest any additional solution/trick ?

(for example, I added capacitor 100nF in parallel with upper feedback resistor, it helps but partially)

the target is that the inrush current should not exceed 3A.

Thanks.

  • 0
    TI__Intellectual 2810 points

    Hi German,

    Thanks for reaching out,
    I noticed you created an identical thread in parallel, therefore, I'll follow you up in this thread, I deleted the other one.
    Please allow me some time to take a look at you question.

    Thank you and best regards,
    Bryan

  • 0 in reply to Bryan Radix
    TI__Intellectual 2810 points

    Hi German,

    Excuse me for the delayed response.
    Is there a reason why you are planning on using the LM3488 over a more recently released solution like the LM5155? The newer components mostly have more elaborate documentation that can help you with your design.

    Furthermore, could you please send me the schematic that you've built so far, it would be great to see the values you've chosen for soft-start, compensation and more.

    Thank you and best regards,
    Bryan

  • 0 in reply to Bryan Radix
    Prodigy 10 points

    Hi Bryan,

    thank you for the reply.

    I started developing new version of our existing project, one of the new features requires DC/DC boost converter, 12v-to-24v.

    after selection LM3488 - I proceeded to PCB layout phase, so we have now first "trial PCBs", we prefer to try these design,

       even though the issue with inrush current....

    I would like to improve the design based on LM3488.

    (if it will not be successful, then we can consider another IC, of course)

    so, the main issue is that this design, suggested by WeBench - suffers of spike inrush current that exceeds 5A.

    I would appreciate your comments regarding any improvement or solution.

    see schematic below.

    Thanks.

  • +1 in reply to German Shevchuk
    TI__Mastermind 46971 points

    Hi German,

    all Boost converter have an initial pass through through the inductor and Diode.

    Through that you have an initial inrush current spike when the output capacitors are loaded to the voltage level of the input voltage.
    Only after that the softstart will take care about a slower ramp with an controlled inrush current during voltage ramp up to the boost voltage level.

    The LM5121 is a controller which has an additional control of the incrush current.

    Best regards,

     Stefan