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TPS922053DYYREVM: Is there any way to accelerate LED current rise/fall time?

Kazuya Nakai59
Guru 20760 points
Part Number: TPS922053DYYREVM
Other Parts Discussed in Thread: TPS922053, TPS92641

Tool/software:

Hello Steven,

Thank you very much for your supports.

I measured LED current rise/fall time using TPS922053 EVM.
I attached a LED current waveform.

I have the following questions about the attached waveform.

Q1.
Is there any way to accelerate LED current rise/fall time?
Because one of my customers needs 1us and 2A LED on pulse for machine vision.

Q2.
Their conditions are Vin=12V, Vf=3.2V, If=2A.
Can TPS922053 generate 1us one shot pulse with 2A ?

Thank you again and best regards,
Kazuya.  TPS922053EVM_LEDon_ off.pdf

  • 0
    TI__Mastermind 19395 points

    Hi Kazuya,

    A1. Some ways to accelerate LED current rising / falling time include:

    • Use inductor with smaller inductance value (You need to increase the switching frequency accordingly in order to maintain same amount of inductor current ripple.).
    • Use output capacitors with smaller capacitance value.

    A2. May I understand what is customer's requirement on output current rising / falling time? Is there any requirement on the output current ripple?

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Guru 20760 points

    Hi Steven,

    Thank you very much for your reply.

    About A2, They want to generate1us pulse width with 2A. So rise/fall time should be less than 1us.
    Also LED ripple current would be less than 50%.

    Could I ask you one question as the below?

    Q.
    Are there any example of outputting with 1us, 2A one pulse using TPS922053?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 19395 points

    Hi Kazuya,

    Kazuya Nakai59 said:
    Also LED ripple current would be less than 50%.

    I assume the current ripple you mentioned refers to peak-to-peak current. Please correct me if I am wrong.

    If this is the case, then for TPS922053, customer can try below settings:

    • Change the switching frequency to 2.2MHz.
    • Change the inductor to 1.5uH
    • Change the output capacitor to smaller value like 10nF
    • Disable the thermal foldback function by setting the R_TEMP to 0ohm. (The switching frequency is very high. Therefore, the SOT-23-THN package may be very hot to trigger the thermal foldback function.  Let's disable this function at this time for easier test.)

    Please check the results. If this resulted current rising / falling time still does not satisfy the customer's requirement, then the customer can consider using the shunt FET PWM dimming feature of TPS92641, which is much easier to achieve 1us current pulse time at such condition.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    TI__Mastermind 19395 points

    Hi Kazuya,

    One note for you:

    Steven Li said:

    A1. Some ways to accelerate LED current rising / falling time include:

    • Use inductor with smaller inductance value (You need to increase the switching frequency accordingly in order to maintain same amount of inductor current ripple.).
    • Use output capacitors with smaller capacitance value.

    With the second way, you may need to increase the switching frequency or the inductance value of the inductor accordingly in order to maintain the same amount of output current ripple since you use output capacitors with smaller capacitance value here.

    Best Regards,

    Steven