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TPS922052: Question about high speed ILED transient waveform.

Kazuya Nakai59
Guru 20815 points
Part Number: TPS922052

Hello guys,

One of my customer is considering using TPS922052 for their new products.

At this moment, they have the following question about this device.
Could you please give me your reply?

Q.
TPS922052 datasheet says that this device can driver LED with 150ns pulse width.
They want to see a waveform when LED current is being driven with 150ns pulse width.
Could you please send me a example waveform?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Mastermind 20020 points

    Hi Kazuya,

    The 150ns we mention in the datasheet refers to the minimum PWM on time that the IC can recognize and therefore the internal switching FET can take action. Please refer to Section 7.5 Electrical Characteristics from the datasheet.

    The idea minimum current pulse width is 150ns if we only consider how fast the IC can react. However, in real situation, it is very hard to produce a perfect square wave of 150ns current pulse since there is always an inductor and output capacitors, which will limit the current rise / fall time.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Guru 20815 points

    Hi Steven,

    Thank you very much for your reply.

    I understood that the 150ns means the minimum time which the device can react not LED current pulse width.
    Could I ask you an additional question?

    Q.
    After the device starts operating when the EN/PWN signal going high, what is the maximum on-duty of the SW pin to increase LED current to the target current? Is it 100% on duty like DCS method of TI DCDC converter control method?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 20020 points

    Hi Kazuya,

    I am currently out of office. I will reply to you later today when I am back to office. Thanks for your understanding.

    Best Regards,

    Steven

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 20020 points

    Hi Kazuya,

    Kazuya Nakai59 said:
    Q.
    After the device starts operating when the EN/PWN signal going high, what is the maximum on-duty of the SW pin to increase LED current to the target current? Is it 100% on duty like DCS method of TI DCDC converter control method?

    Sorry but I am not familiar with DCS-Control.

    The control mode of TPS922052 is adaptive off-time current mode. For TPS922052, after the device already starts up (so that we can assume the soft start is over), when EN/PWM goes from low to high, the switching FET will turn on. The FET will keep on until the current goes through it reaches the peak current level determined by the COMP pin. 

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Guru 20815 points

    Hi Steven,

    Thank you very much for your reply

    I understood that TPS922052 switching FET will keep on until the current goes through it reaches the peak current level determined by the COMP pin. 

    This is the function I wanted for a rapid current rising.

    Thank you again and best regards,
    Kazuya,

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 20020 points

    Hi Kazuya,

    You are welcome. I am going to close this thread. Please feel free to contact me again if you have any further question.

    Best Regards,

    Steven