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Documentation for LMR70503

Other Parts Discussed in Thread: LMR70503

      I am using the LMR70503 for a negative supply. In the datasheet it calls out a 6.8uH coil in the Application Circuit Bill of Materials. I looked at the datasheet for this coil and the current and resistance ratings that are mentioned in the LMR70503 datasheet do not match the ratings for the VLS2012ET-6R8M datasheet. I just wanted to point this out. The ratings in the coil's datasheet are lower current and higher resistance (.64A typical and .415 Ohms typical). Is this still ok for the LMR70503 application? Please clarify this.

Thank you,

Michael Nycz

  • We've received your query and will get back to you shortly.

    Thanks,
    Anston
  • Hi Michael,

    There should be no problem using this inductor, however I need to know your input and output voltages and currents to be sure.

    Thanks,
    Anston
  • Hi Anston,

    I am providing a +5.0V input voltage and configuring the LMR70503 for a -1.5V output. The max current I expect to draw is 200mA. I am using the LMR70503 to drive the EA BIAS for an Avago TOSA device (actually, four of them).

    Thank you,

    Mike Nycz

  • Hi Mike,

    I ran it through my circuit calculator and you have plenty of margin to spare even after derating for the less than ideal inductor values. I assumed 55% efficiency worst case, for your conditions and for DCR of the inductor at 415mOhms, the maximum current output will still be ~210mA which is above your specification and the inductor will still have margin from saturation.

    You can swap the inductor for a better DCR value, I would recommend it if there is a possibility of pushing your application beyond 200mA or for transient headroom.

    Thanks,
    Anston