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TPS922053: Change dimming mode during fading of TPS922053 or TPS92205x

JOOHYEONG KIM
Prodigy 20 points
Part Number: TPS922053

Hi, I'm Kim.

Hybrid dimming mode has some issues at lower dimming levels because it operates at 8-bit resolution.

So I want to control follows :

Brightness 100% ~ 10% : hybrid dimming mode

Brightness 10% ~ 0.1% : PWM dimming mode

 

For example, if the fading time is 4 seconds and the fade down from 100% to 0%,
is there a way to naturally switch from hybrid dimming mode to PWM dimming mode while fading?

  • 0
    TI__Mastermind 23150 points

    Hi Kim,

    You cannot switch between PWM dimming mode and hybrid dimming mode unless you disable the IC first, then re-enable it and select the new dimming mode.

    JOOHYEONG KIM said:
    Hybrid dimming mode has some issues at lower dimming levels because it operates at 8-bit resolution.

    May I understand what are the issues you encountered?

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    When the PWM dimming mode, it was makes some sound noise.

    And when the hybrid mode, Max

    Steven Li said:
    수

    The 100% output of our product is 1A, and the step phenomenon of the output current is visible at low dimming levels.
    For example, even if PWM/EN is controlled with 15bit pwm duty at 1kHz,
    It feels like it operates from 0% to 0.1%, from 0.1% to 0.5%, and also from 0.5% to 0.9%.
    Of course, I know that this is a feature of the hybrid mode of this IC.

  • +1 in reply to JOOHYEONG KIM
    TI__Mastermind 23150 points

    Hi Kim,

    We do not recommend customer use hybrid dimming mode with more than 8-bit resolution (i.e., 256 steps) since the internal PWM signal has a 0.4% hysteresis response when the PWM input duty cycle changes between increasing and decreasing in hybrid dimming mode. Please refer to Section 8.3.5.3 Hybrid Dimming from the datasheet.

    JOOHYEONG KIM said:
    It feels like it operates from 0% to 0.1%, from 0.1% to 0.5%, and also from 0.5% to 0.9%.

    Based on your description, most likely the 0.4% step you observed here is due to the 0.4% hysteresis response mentioned in the datasheet.

    If you want analog dimming at 100% ~ 10% brightness and PWM dimming at 10% ~ 0.1% brightness, you should use flexible dimming mode (i.e. use two pins, EN/PWM pin and ADIM/HD pin, to do the dimming).

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    Hi Steven,

    I was read your advice.

    I will do that flexible dimming mode test.

    Best Regards,

    Kim.

  • 0 in reply to JOOHYEONG KIM
    TI__Mastermind 23150 points

    Hi Kim,

    Noted. I add more comments on my last reply for your reference.

    Please feel free to contact me again if you have any further question.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    Hi Steven

    It is a bit unfortunate that there is a time loss of about 2 msec for dimming mode start,

    but the sample was produced to an almost satisfactory level through flexible dimming mode.

    Best Regards,

    Kim

  • 0 in reply to JOOHYEONG KIM
    TI__Mastermind 23150 points

    Hi Kim,

    Could you please provide more information about the 2ms time loss? Do you have any oscilloscope capture that can illustrate this time loss?

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    Capturing is possible, but let me explain first.
    To make LAMP operate like 100% -> 50% -> 30% -> 0%
    Even if the lighting is initially turned on to 100%, it must be started in flexible dimming mode, so random pulses of 3 to 4 cycles(2khz) are output to ADIM/HD and EN/PWM and control begins.

    Of course, I am satisfied with the current situation.

    Best Regards,

    Kim.

  • 0 in reply to JOOHYEONG KIM
    TI__Mastermind 23150 points

    Hi Kim,

    JOOHYEONG KIM said:
    Of course, I am satisfied with the current situation.

    Glad to hear that. If you want to see if there is any possibility of improvement, please kindly share the oscilloscope capture to help me understand what is happening.

    Best Regards,

    Steven