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Original question:

[FAQ] How to get a quick transition of TPS923655 / TPS923654 / TPS923653 / TPS923652 from shutdown into flexible dimming...

TPS923654: Flexible dimming mode - Brightness and On/Off Control

Tylor
Prodigy 200 points
Other Parts Discussed in Thread: TPS923654

Tool/software:

Hi,

We are using TPS923654 for controlling LED. Tried to utilize flexible dimming mode to control the LED brightness and ON/OFF control independently. Is it  possible to control On/Off from 0Hz - 120Hz with PWM signal on EN/PWM pin and Brightness with PWM signal on ADIM/HD pin. We also face problem with Flexible dimming mode selection. Followed this article but failed to activate.

  • 0
    TI__Mastermind 30451 points

    Dear Sir,

    Thanks for reaching out! I will check your question and get back to you during these days. Thank you!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Mastermind 30451 points

    Dear Sir,

    If you look into the FAQ, there will be a detailed description about how to enter the flexible dimming mode from shutdown. Could you pls kindly follow the guidance?

    Firstly, you need to follow the startup sequence shown in Section 8.3.4 and Figure 8-2 from the datasheet so that the device will be ready for dimming mode selection ("Dimming Mode Start" = high). This step cannot be accelerated.

    Secondly, normally you need time for the device to identify and select the flexible dimming mode with ADIM/HD pin = high for at least 1.5us. Then the device will undergo a soft-start time to let the reference voltage V_REF rise to the target value. This step can be accelerated by following the below method:

    • After the device is ready for dimming mode selection, you need to input 1.5% Duty, 10kHz PWM for at least 4 periods to the ADIM/HD pin. Then the soft start will end and the device will be ready to get your ADIM/HD and EN/PWM input.

    I am not sure why you failed this configuration. Do you mean that you will not see the LED going from dark to dim?

    Thank you!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    Prodigy 200 points

    We tried to restart the dimming mode selection by pulling enable to low for 100ms and a high level for 100uS then bring it low level(to create the scenario EN=High aftrer Vin > Vin_uvlo) - wait for 300 us and start PWM signal at 10KHz on ADIM pin. Did we miss anything here ? Also i couldn't find the picture used in this response anywhere in the datasheet. Is there any additional document has detailed information about mode selection?


    Another important doubt which i would like to clarify first before debugging the issue further. With Flexible(or anyother) mode, Is it possible to control the LED toggling at different frequency(0-120Hz) with PWM sign on PWM pin and control brightness with PWM sign on ADIM Pin?

  • 0 in reply to Tylor
    TI__Mastermind 30451 points

    Dear Sir,

    I will check your question and get back to you by end of this week. Thank you!

    BRs

    Lucia

  • 0 in reply to Tylor
    TI__Mastermind 30451 points

    Dear Tylor,

    Yes, in theory it will be no problem to support this. The LED current value and the on/off behavior can be controlled independently. But pls be noted that if stop inputting PWM into EN/PWM pin longer than tPWM_IN_OFF (57-77ms), the device will go into shutdown status. When the next EN/PWM pulse comes, the device still needs to go over above startup sequence + mode selection requirements.

    Tylor said:
    possible to control the LED toggling at different frequency(0-120Hz) with PWM sign on PWM pin and control brightness with PWM sign on ADIM Pin?

    There is no problem of the EN/PWM signal configuration. And for 10kHz ADIM signal, what is the duty cycle of it?

    Tylor said:
    We tried to restart the dimming mode selection by pulling enable to low for 100ms and a high level for 100uS then bring it low level(to create the scenario EN=High aftrer Vin > Vin_uvlo) - wait for 300 us and start PWM signal at 10KHz on ADIM pin.

    Additional document currently not available. But any question related to it, you can let us know.

    Tylor said:
    Also i couldn't find the picture used in this response anywhere in the datasheet. Is there any additional document has detailed information about mode selection?

    It would be really appreciated if you could send us a diagram to illustrate the EN/PWM and ADIM signal in same figure. And you also mention that it failed to active, not sure whether it means that you will never see the LED begin to dim up.

    Thank you!

    BRs

    Lucia