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LM3410XMFLEDEV: Switching frequency is 1.17MHz?

ArTzy
Genius 16570 points
Part Number: LM3410XMFLEDEV
Other Parts Discussed in Thread: LM3410

Hi Experts,

Seeking your assistance on this query:

1. The frequency of the SW i tested is 1.17 Mhz around not as the datasheet shows 1.6Mhz. As the picture showed below (I tested the Pin1 of LM3410x(sot23 pack))


2. As datasheet says, Rled = Vfb/ Ifb.  but as i tested, the Vfb changed with the Rled. Means if i use 220mohm Rled for test, the Vfb equals 66mV, then i change Rled to 300mohm, Vfb changes to 99mV either. That seems the Vfb is fluctuated and the power of the LED drive is fixed.
3. I post my design here for your reference.
Thank you.
Regards,
Archie A.
  • 0
    TI__Genius 9630 points

    hello ArTzy

    1. for the frequency, did customer zoom in to see the frequency by cursor? As the frequency range given in the datasheet is 1.2MHz to 2MHz with 1.6MHz typical. This piece of device may be at lower position.

    2. looks like the operation triggers current limit, what are the values of input and output voltages?

  • 0 in reply to Mason Wang
    TI__Genius 16570 points

    Hi Mason,

    Thanks for guiding. Cx shared:

    1. I changed 3 pieces of LM3410 and the results are the same...
    2. The datasheet said the typical value is 1.6Mhz and min/max value are 1.2/2.0 MHz means in the different temperature condintion will casue the different frequeccy, Not the piece by piece division I guess. As the pic shows on datasheet page 7 figure 7.
    3. The input voltage is 5V by power bank and output voltage should be 6.2V(LED @ 700mA ). I set Rset as  220mohm/300mohm/1 ohm respectively and the frequency as the same(1.17Mhz around). Vfb equals 60mv@220mohm 90mv@330mohm and 100mv @1ohm.The frequency is constantly 1.17Mhz around.
    Any suggestion about the frequency and the Vfb? How can we check the validations of the chips and our circuits?
    Regards,
    Archie A.
  • 0 in reply to ArTzy
    TI__Genius 9630 points

    Hello Archie

    I would like to require more waveforms: SW(with duty cycle and frequency), Vout, inductor current.

    pls try to increase output voltage to 12V and see any difference.

  • +1 in reply to Mason Wang
    TI__Genius 16570 points

    Hi Mason,

    Thanks for your support.

    The customer found out that they bought the fake one. Got a new chip from another local distributor, installed it and tested it, everything's back. frequency back to 1.6Mhz and Vfb back to 190mV.

    Thank you.

    Regards,
    Archie A.

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