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TPS92520-Q1: Can this device drive LED string with 20mA?

John11513
Expert 5720 points
Part Number: TPS92520-Q1

Hi Experts,

I am wondered if this device can be used to drive low power LED string with only 20mA current? I understand this device is over-spec for this kind of requirement, however my customer like its functional safety capability feature very much and they are not very cost sensitive, it will be very good solution for my customer's application if it can support 20mA output (for each channel).

Thank you!

John

  • 0
    TI__Mastermind 23226 points

    Hello John,

    Yes the TPS92520 can support lower currents.  You may need to change the sense resistor to optimize it.  If you have information about the input voltage range, range of LEDs used, information about LEDs, LED current range, desired switching frequency.  Once I have this information then I can recommend component values or if they might want to consider other LED drivers.  

    -Francis Houde

  • 0 in reply to fhoude
    TI__Expert 5720 points

    Hi Francis,

    Thank you so much for your quickly reply!

    Here is the application information:

    Input voltage range: 40V to 60V;

    Vf of single LED: 1.5V to 3.2V;

    number of LEDs in each string: 12 LEDs; (there are totally 8 strings per system)

    LED current: 20mA or 40mA; ( no need for dimming, fixed 20/40mA constant current driving is required)

    fsw: no specific preference, smaller size is preferred while need considering EMI.

    Other drivers are also welcome. They are not cost sensitive but require functional safety.

    Thank you!

    John

  • 0 in reply to John11513
    TI__Mastermind 23226 points

    Hello John,

    Is the 40 to 60V supply the only supply?  Are there other rails available.  This is pretty small output power ~1.5W per channel for a total output power of ~12W.  You could look at boost or Sepic devices instead of buck if you have lower supply rails and yet still be automotive.

    -Francis Houde

  • 0 in reply to fhoude
    TI__Expert 5720 points

    Yes, other rails is also possible. Do you think this device is not the best solution? Which device is best solution do you think? (without consideration of cost and power rails)

    There are another two special requirements for this application:

    1. The input power is not continue. Actually the input supply is turned off 40ms every 100ms, while the LED has to lighting continually. A bulk cap is used to power the LED during off time. (this is the reason why choose 40V to 60V input range)

    2. Fail safe feature. The system has to ensure fail safe. Means in any failure mode, MCU must ensure reliably turn off the LED.

    Thank you!

    John

  • 0 in reply to John11513
    TI__Expert 3630 points

    John,

    You will get a response shortly

    Thanks

    Sumeet

  • 0 in reply to John11513
    TI__Mastermind 23226 points

    Hello John,

    1)  I now understand the desire to operate at higher voltages because of the ability to store more energy in the bulk capacitor (0.5*C*V2).  It would be good to get more information about the application.   

    2)  I need to more information about fail safe mode.  Are you assuming that the MCU is still alive during this failure modes?  If that is the case, then there are other parts that can do this.  If you have to ensure it that the devices turns off during a fault such as lost of communications then this part is well suited because of the watch dog timer and being able to setup the Limp Home mode of the device such that the channels are off.  

    It might be better to talk offline and get more information about this application.  Please friend request me and include your email address so we can take this offline.

    -Francis Houde