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LMR16006Y-Q1: Does minimum ON time requirement apply to fixed output part number?

Bruno Saraiva
Guru 13040 points
Part Number: LMR16006Y-Q1

Fellows,

To better understand this issue, the post below is a relevant background.

e2e.ti.com/.../629093

As a summary, it appears that LMR16006Y can not be selected for a 36V input, 3.3V output, because minimum on time requirement would not be met.

Following TI's response on the above thread, we redesigned several of our boards to use LMR14006X. Now, due to the fact that 14006 seems not to be available anywhere in the planet for the next 4 months, we looked again for alternatives.

That is when I noted that there is a FIXED OUTPUT LMR16006Y, said to be good for 4-40V input, fixed 3V3 out.

Either the reply to the previous post is incorrect (in which case, Webench parameters are wrong), or LMR16006Y has an invalid range within what is described as its operating parameters. Which one is the case?

Thanks

Bruno

  • 0
    TI__Genius 11040 points

    Hi Bruno,

    Thank you for sharing the background on this post.

    As discussed in your previous thread, WEBENCH will limit the part options based on the minimum on time.  If the on time could potentially be below the minimum on time, then WEBENCH will not recommend this device.  This is the case with the LMR16006Y at 3.3Vout, Vin=4V-36V.

    However, as you pointed out the LMR16006Y datasheet specifies Vin=4-40V for the recommended operation conditions.  Within this input voltage range, the device can be enabled and switching.  

    If Vin> approximately 19V, then the LMR16006Y device will be operating at the minimum on time limitation.  The LMR16006Y will have an increased output ripple and will operate in pulse skipping mode (an example is pictured below).  

    Please let me know if you have any additional questions.

    Best Regards,

    Katelyn Wiggenhorn

  • 0 in reply to Katelyn Wiggenhorn
    Guru 13040 points

    Hello Katelyn,

    Thanks for such a detailed answer, particularly for taking the time and generating a scope capture of the power line.

    We will go on and keep the design using the 16006Y. Our most usual DC input for that line will be ~24V, but we do need the range to be from 12 to 38.

    Seeing your scope print, we can (kind of) consider in that situation that the switching frequency will be much less than the nominal. Would it be a good idea to use a somewhat stronger inductor?

    Also, to be on the safe side, a bit more of capacitance is probable useful as well, right?

    Regards

    Bruno