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TPS92633-Q1: Current Source or Current Sink LED driver

Charan Bandikatla
Prodigy 50 points
Part Number: TPS92633-Q1

Tool/software:

Hi i'm working on rear lighting for an automotive application. I want to select a LED driver for my application. But i'm not able to decide between constant current or constant source LED driver.
Can you please explain on what basis this should be decided. Please explain explain in detail the problems that may be faced when using a current source over current sink and vice versa.

  • +1
    TI__Genius 10325 points

    Hi Charan,

    This is a complicated question. Can you give us more information on your architecture? The current source is useful if you want a common cathode (i.e. single wire back for ground/chassis). If you want common anode (single wire for supply), then a sink makes sense.

    Current sinks are often smaller and less expensive because they use N-channel FETs which have a lower RDS-on for the same die area compared to a P-channel.

    Are you using battery voltage or buck regulated voltage? What is the current requirement? If you are using a pre-regulator buck to step down battery voltage, you already have a common anode supply and the lower cost current sinks make sense.

    Regards,

    Zach

  • 0 in reply to Zach Olson
    Prodigy 50 points

    I'm designing a rear combination Light for automotive. I'm stacking 2 red leds per string using several strings. I have LEDs on seperate PCB. Driver and MCU are on main controller board. I have a Kl30 supply and i'm using a buck to generate VLED supply of 9V. Here both current sink and source either fulfills my output requirement. Just wanted to understand whether there is any strong reason to choose between current source or sink.

  • 0 in reply to Charan Bandikatla
    TI__Genius 10325 points

    Hi Charan,

    Thanks for the additional information. There is not always a strong reason to choose one or the other, it really depends on the specific architecture.

    Typically, our current-sinks require a 3V-5V supply. This may not be an issue in your system as your driver is on the same board as your MCU which I assume takes 3.3V or 5V supply as well.

    The current-sources can typically operate between 4.5V-40V supply which provides more flexibility. In your system, you can connect a current-source driver directly to the 9V buck supply which can simplify the power distribution in your system. High-side drivers can also have advantages in certain fault conditions such as short-to-supply because of the higher voltage rating.

    Something like TPS92633-Q1 with external thermal sharing and off-board binning control is a really good option for LEDs on separate PCB. The external thermal sharing may be especially useful to spread out the power dissipation as you are operating multiple 2-LED strings on a 9V supply.

    https://www.ti.com/product/TPS92633-Q1

    I've linked below our parametric search tool for both current-source and current-sink automotive LED drivers.

    https://www.ti.com/power-management/led-drivers/automotive-led-drivers/products.html#1129=Current%20Source& 

    https://www.ti.com/power-management/led-drivers/automotive-led-drivers/products.html#1129=Current%20Sink& 

    Regards,

    Zach