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TPS92690: What is the maximum PWM dimming frequency controlled by nDIM terminal?

Kazuya Nakai59
Guru 21505 points
Part Number: TPS92690
Other Parts Discussed in Thread: LM3423, TPS92691, TPS92692

 Hello guys,

 One of our customers is considering using TPS92690. They have the following questions. Could you please give me your reply or any comment?

1. What is the maximum PWM dimming frequency range controlled by nDIM terminal?

   According to the device EVM user's Guide, it seems that the range is 120 Hz ~ 1000Hz. Is the maximum frequency 1000Hz?

2. What is the maximum and minimum PWM dimming on duty(%) controlled by nDIM.

  According to the device EVM user's Guide, it seems that the range is 5%~ 95% at 200Hz. Do you have any data about on duty?

3.  They think LM3423 is a similar device with TPS92662. Which device can operate with higher frequency for PWM dimming controlled by nDIM terminal?

     Are both PWM dimming frequency similar? Are those about 1kHz?

4. Is there any boost type LED driver can operate for higher PWM dimming frequency?   

 Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.

 

  • 0
    TI__Mastermind 25500 points

    Hello Kazuya,

    To answer your questions:

    1. That is a recommended frequency range to have good linearity and dimming range. With this device you are somewhat limited by the current rise/fall times. So you can go higher than 1kHz but you will have lower linearity and more limited minimum duty cycle.

    2. Max is 100%, min is really determined by the current rise/fall times so it is specific to each application.

    3/4. The LM3423 can dim faster since it uses an output capacitor disconnect FET to keep it charged up for the next cycle. The TPS92691 or TPS92692 can also dim significantly faster for the same reason. But any boost converter will be more limited in frequency than a buck converter. I have seen these devices used up to 30kHz for applications that don't need extremely low duty cycles. But as with any PWM dimming the lower the frequency the better the dimming range.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 21505 points
    Hello Clinton,
    Thank you very much for your prompt reply.
    Your reply is really helpful for our customer and me.

    Thank you again and best regards,
    Kazuya Nakai.