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LM3429: LM3429 data sheet contradiction

Part Number: LM3429

we have a heat problem with the LM3429 when  running 

it with Vin from 7.2 to 6V. With 12V it is ok. I understand that, judging from the data sheet that both

the 12V and the lower range is outside guaranteed specs. I must therefore try to establish the source

of this extra heat. Is it possible that the heat comes from the chip operating poutside of guaranteed

specs? In the datasheet it says that it can withstand the range 4.5 to 75V, BUT that recommended

range is at least 10V as Vin, not lower. How i that contradiction to be interpreted?

I highly appreciate a fast response since the LM3429 is located in a Product that is used

in security calssified Environments and we need to find the cause of the extra heat. We have

understood by using a simulation of the LT3477 that the internal resistance of the switch inductance

is one part of the problem since when operatin down to 6V you get high switch current.

  • Hi Zachariaz,

    I cannot comment on the LT part. In general, at lower voltage you will require higher switching current to deliver the same output power therefore the switching FET will experience higher power dissipation and that is normal for power transfer circuit.

    Thanks Tuan
  • Hi Tuan

    when running testst Ican see that at Vin=12V I have a PRF abt 40kHz, Iout=480mA. When goinf down to

    7V the PRF goes up to 550kHz, putting a considerable strain on the LEDs due to the higher actual current that

    the high PRF results in. The PRF voltage peaks are corresnping to 1.6Amps meaning 3 times more than they

    were designed for.

    This must mean that the LM3429 cannot operate below recommended 14V (in our case 12V works fine). But 7V

    is definitely not recommended, even though you have 6-12V in an appnote. Has anyone at TI cpnsidered what

    the high PRF pulses do to theload?



  • Hi Zacharias,

    What do you mean by PRF and if it means switching frequency then how does that put stress on the LED if the current is controlled to what it needs to be?

    As I mentioned as input voltage goes down the input current needs to go up in order to deliver the same output power.

    If there is something that you do not really understand then please clarify and send schematic along with scope captures with needed questions and we will fo our best to answer you.

    Thanks Tuan