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TPS92518: The problem of TPS92518 PWM dimming

Eagle.Miao
Intellectual 910 points
Part Number: TPS92518

The problem of TPS92518 PWM dimming is as follows:

 

1. The PWM mode of the chip directly modulates the chip so that it cannot be dimmed after adding a PWM wave of 1KHz~2MHz.

    Are there any other parameters that need to be configured (primarily the frequency is already in range)?What are the configuration requirements on the hardware?

    Please help to see the reason. Thank you very much.

2. Can SPI and PWM dimming be carried out synchronously? Are there any operation steps?

  • 0
    TI__Mastermind 28655 points
    Hello,

    1) I'm not sure I understand your question. The 1 KHz - 2 MHz stated in the datasheet is for switching frequency range. If you are PWM dimming via the PWM pin what else are you trying to do at the same time? There is enable dimming, shunt FET dimming and analog dimming.

    2) You should be able to change the Peak current threshold while externally PWM dimming, this would be a combination of analog dimming and PWM dimming.

    You can also set it up for enable dimming and shunt fet dimming.

    Regards,
  • 0 in reply to Irwin Nederbragt
    Intellectual 910 points
    hi，
    How to PWM dimming, can we have a step, we tried the PWM light cannot work.
  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points

    Hello ,

    1) Now I want to use a combination of analog dimming and PWM dimming ,can it work through the following method:

    1. Through SPI  communication  to adjust LEDx_PKTH_DAC and LEDx_TOFF_DAC .

    2. Then add PWM signal to the device .

    2)  The datasheet describes  10000:1 for PWM ，is it relevant to PWM frequency(how to configure it ) ?

  • 0 in reply to user5534304
    TI__Intellectual 2935 points

    Hi,

    Pls see the datasheet.

    The TPS92518 has been designed to support three dimming methods. Analog, PWM and Shunt-FET or Matrix (TPS92661/TPS92662 device family) dimming. Analog dimming is still accomplished via the SPI interface through adjustment of the LEDx_PKTH_DAC register. PWM dimming is accomplished by using the PWMx pin.
    Shunt-FET or Matrix Dimming is optimized by using the LEDx_MAXOFF_DAC register. One or more dimming methods may also be combined to obtain extreme contrast ratios.


    2) It mean the external PWM(Not the PWM for the DC-DC) for the PWM Dimming.

  • 0 in reply to Wu JW
    Prodigy 20 points
    Thanks for your reply ,now i am using a combination of PWM dimming and Analog Dimming .I have Implemented each method ,but a situation is when i use Analog diming to control led ,PWMx pin must keep a high level .Can you give me a suggestion about this situation ?
  • 0 in reply to user5534304
    TI__Mastermind 28655 points

    Hello,

    That is how it is supposed to work.  If PWM is high it regulates to the PK current threshold.  If PWM is low it is basically near zero output.

    If you have PWM set to 50% and the peak current threshold is set to 255, you will get an average of 50% of full current.  If you lower the peak current threshold to a lower value when the PWM is set to 50% you will get a lower average current.  This is how you get more dimming resolution.

    Regards,