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Suitable part for high current LED driver

Morten Hjerde
Prodigy 200 points
Other Parts Discussed in Thread: LM3409, TPS92641

We are looking for a suggestion for suitable parts for a new design.

Design requirements for the new LED driver:

Buck
V(in-nom) 48V
Vf(led) 30-40V
I(led) 6A
f(PWM) 20kHz

The configuration is 6 separate LED channels (LED colors). All channels are PWM controlled in real-time to produce the desired spectrum and most of the channels are active at any given time.
The Vf of the strings are 30-40V as mentioned above and there may be parallel strings.

We need to dim to a low brightness (0.1%) without noticeable change to the spectrum (we have techniques to increase linearity at low brightness). Hardware linearity to 0.1% of a 20kHz PWM duty cycle is probably out of the question. What is the shortest current pulses achievable?

We are not new to LED drivers. Our existing designs are mostly based on the LM3409 from TI. We now need more current than we can get from the LM3409.
The advantage of the LM3409 is that it is fast and can be made more precise with a shunt FET.

We are looking for a suggestion for suitable parts for this new design.
We will require higher power in upcoming products and it would be great if the same part could be used.

  • 0
    Prodigy 200 points

    To clarify: I am not expecting to find one driver that can control all channels. We are fine with individual drivers, i.e. one for each channel.

  • 0 in reply to Morten Hjerde
    TI__Genius 9630 points

    Hello Morten

    would you mind sharing your application here? 

    actually Lm3409 can still fit for the application as you know it is a LED controller that does not integrate power FET. The only thing that limits the current rating is the driving current capability of the device. 1A driving current of LM3409 can still deal with power FET supporting 6A application.

    we now have new device integrating FET with quite good fast dimming performance but can only supporting 4A for one device. If there is other application with lower current rating, I would highly recommend this.

  • 0 in reply to Mason Wang
    Prodigy 200 points

    Hi Mason

    The application is a light used in video production, film and broadcast. You can see one here: https://www.kelvinlight.com/
    We have high requirements for the quality of white light, the ability to dim to a low brightness without color drift, flicker free, wide color gamut, etc, etc.
    We build the spectrum from distinct colors, no white LEDs involved.

    LM3409 has served us well and we love it. One challenge when using the LM3409 is finding PMOS transistors that perform well at higher currents. Let alone sourcing them in volume.

    For future developments it would seem like the TPS92641 is better suited for higher power. As it is a sync buck device. The power loss and thermal challenge will get very high for the LM3409, do you agree?

  • 0 in reply to Morten Hjerde
    TI__Genius 9630 points

    hello Morten

    thanks for your information. 

    The thermal condition of LM3409 should be fine since the power Fet is external and driving loss for LM3409 will not increase much for 6A PMOS transistor. I think if PMOS is properly chosen, LM3409 can still fit for the application. 

    TPS92641 has the same driving capability as LM3409 with 2ohm 1A so it is also a candidate for this application. As it is a sync topology, I agree that system thermal condition should be better than LM3409 but possibly with higher bom cost due to additional power fet. 

  • 0 in reply to Mason Wang
    TI__Genius 9630 points

    I will close this thread if no more questions.