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Can the LT8613 operate as a current-mode LED driver?

Category: Hardware
Product Number: LT8613

Hi,

I am trying to design a current-mode LED driver that runs with Vin from 3.5-4V, and drives a LED with Vout 2.8-3.4V with a max current of 6A. The LT8613 came up in a search but it's not exactly clear if it will operate in this mode. I was thinking of programming the voltage feedback resistors to give 4V, and use the current sense resistor to control the output current to the LED, and using the ICTRL pin to adjust the operating current.

A related question is what will happen if the Vin drops below the Vout, in other words if the battery gets low enough that it can't supply the current being requested.

Thanks,

Lloyd

  • I’ve got the same question too. Have you tried testing this configuration yet? Does it work properly?

  • Hi   That was 3 years ago, and I didn't end up using that part. The fundamental thing I learned on that project is that trying to do buck/boost or boost at high currents using a battery is a bad idea. As the battery voltage drops, the boost tries to draw an impossible amount of current and the battery voltage collapses. I used the LT8642 (a voltage output device) with an external current sense amp to make it be a current source (which is what an LED needs). That has worked very well.

    In the case where I needed a buck with an LED, it was a nightmare. I had to run hundreds of experiments to find out what the safe operating limits of battery voltage and output current were in my application, then use firmware to keep away from that limit where the battery would freak out from having too much current pulled from it.

  • Hi,
    For LED driving, these fall under Constant Current vs. Constant Voltage as the LT8613 is for a regulated power supply. 
    The issue here is your Vin to VLED is very close. 
    I think you need to boost  Vin to something like 10V, then use one of our LED drivers such as the LT8391.
    This is a 4V min LED driver/battery charger. Thus you need a pre-boost. 
    Page 32 of the datasheet is for a 7A battery battery charger, This should work for a 15-20W LED application with some modifications. 

    Best Regards,
    Chris

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