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TPS92640: Control methods

Y.Ottey
Mastermind 6145 points
Part Number: TPS92640

Dear TI Team

My customer is considering dimming the TPS92640 in the following ways: (LED current is up to 500mA)
・ LED current 5mA ~ 500mA:
The LED current is controlled by changing the voltage applied to the IADJ pin while the 100% Duty PWM signal (constant voltage) is input to the UDIM pin.
・ LED current 0mA ~ 5mA
Apply a voltage of about 0.1V to the IADJ pin and control the LED current by changing the duty ratio of the PWM signal input to UDIM.

Please answer the following questions about the above method.
1. If you check the data sheet, only the form that inputs the PWM signal to the UDIM pin and adjusts the LED current by the duty ratio of the input signal is described as shown in the circuit configuration below.
Is there a problem with the control method that changes the voltage applied to the IADJ pin while the UDIM pin is at a constant voltage on the TPS92640?


2. If there is no problem in 1., is it possible that the connected LED flickers when switching between the above two control methods?

  • 0
    TI__Mastermind 22745 points

    Hi Ottey,

        The answer to the first question is Yes! IADJ support analog dimming, you can also use this pin to dimming the brightness.

        The answer to the second question is Yes!. You can use the IADJ to change the current level and use the UDIM pin to change the duty cycle. This hybrid dimming method can achieve a high dimming ratio.

    BR

    Sean

  • 0 in reply to Sean Zhou
    Mastermind 6145 points

    Hi Sean

    Thank you for your reply.

    I understand that the dimming method using IADJ and UDIM shown in the first post is possible.
    I have additional questions.


    The method shown in the first post (listed below) switches at 1% of the maximum LED current.
    When our customers tried the following methods, LED flicker was confirmed when switching.
    Also, when switching at 20% of the maximum LED current (LED current 100mA),
    the LED flicker disappeared.

    Is there a recommended switching timing for the method using the IADJ pin and the UDIM pin?
    If so, I would appreciate it if you could let me know.

    ・ LED current 5mA ~ 500mA:
    The LED current is controlled by changing the voltage applied to the IADJ pin while the 100% Duty PWM signal (constant voltage) is input to the UDIM pin.
    ・ LED current 0mA ~ 5mA
    Apply a voltage of about 0.1V to the IADJ pin and control the LED current by changing the duty ratio of the PWM signal input to UDIM.

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Mastermind 22745 points

    Hi Ottey,

         It is not recommended to use the IADJ pin to adjust between 0mA to 5mA. It is recommended to change the PWM duty cycle for a low current while keeping enough voltage on the IADJ pin.

    BR

    Sean

  • 0 in reply to Sean Zhou
    Mastermind 6145 points

    Hi Sean

    Thank you for your reply.

     "It is not recommended to use the IADJ pin to adjust between 0mA to 5mA. It is recommended to change the PWM duty cycle for a low current while keeping enough voltage on the IADJ pin"

    As mentioned above, how much voltage should be applied to the IADJ pin to control the LED current 0-5mA?
    (When the IADJ pin was maintained near 0.5 V and the PWM duty cycle was changed to control the LED current of 0 to 5 mA, no LED flicker was observed.)

    Regards,

    Y.Ottey

     

  • 0 in reply to Y.Ottey
    TI__Mastermind 22745 points

    Hi Ottey,

         Suggest keeping IADJ more than 0.5V for the light load condition.

    BR

    Sean