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WEBENCH® Tools/TPS92515HV: Analog dimming ??

Thomas Westerhoff
Prodigy 20 points
Part Number: TPS92515HV
Other Parts Discussed in Thread: TPS92513HV, , TPS92513, TPS92515

Tool/software: WEBENCH® Design Tools

I've been trying to build an analog dimmable driver with a TPS92513HV for several days. Unfortunately without success. The driver from the Webbench Designer runs constantly with full ILed, even when connected to VAdj 0V. I want to try the TPS92515HV now. But here I'm already failing because of the input to the Webbench Designer. In contrast to the TPS92513HV, I can enter a dimmberecih here. However, I do not understand the input. Does this mean in the picture below that the dimming range is 10-40% or 40-100%?
Is it possible to build a 350mA driver wirh 5% ILed ripple and dimming from 10 to 100%?

  • 0
    TI__Mastermind 25500 points

    Hello Thomas,

    I am not sure about webench, there are often things in there I don't understand. In any case either device can do 350mA with 5% LED ripple current and dim down to 10% quite easily if designed correctly. If you are seeing no dimming with the TPS92513 circuit with IADJ at 0V then I am guessing you have some combination of high input voltage, low output voltage, and high switching frequency. If you are already running close to the minimum duty cycle (determined by the minimum on time and the switching frequency) and you try to dim it cannot go any farther. In that case you would want to use a lower input, a higher output, and/or a lower switching frequency.

    I would recommend using the datasheet and an EVM rather than webench with either device. Webench can give you a decent starting point, but keep in mind the minimum on time and duty cycle when selecting the switching frequency. If you really need a high switching frequency, high input voltage, and low LED stack voltage so that the analog dimming is limited you may want to consider PWM dimming if that is an option.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 20 points
    Hello Clinton

    In the TPS92513 Design the VIN range was from 33 to 48V. Vout was about 30V. With inductivities 39µH to 100µH I tired switching frequencies of 150kHz where I got about 30% Ripple!! but could dimm well. With switching frequencies of about 570kHz The ripple goes down to 10% but dimming was nt possible.
  • 0 in reply to Thomas Westerhoff
    TI__Mastermind 25500 points

    Hello Thomas,

    Sometimes you need to use a lower frequency for analog dimming and use more output capacitance to reduce the LED current ripple. I am surprised it isn't working at those specs at 570kHz however. I would need to see it on the bench to be sure why.

    In any case you may still want to consider the TPS92515 if you need a higher nominal switching frequency. It will actually lower the switching frequency as you dim so often it can give you better range with the same operating conditions.

    Regards,

    Clint