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TPS61500: Analog dimming frequency.

watanabe
Expert 1740 points
Part Number: TPS61500
Other Parts Discussed in Thread: TPS61197

Hi,

My customer has a question.

English data sheet P4 6.3 Recommended Operating Conditions,
"Analog and PWM dimming frequency 200 to 1000 Hz" is stated.
Does this frequency apply only to PWM dimming?

P16 Figure 9. Analog Dimming Linearity shows that,
There are descriptions "PWM Frequency 200 Hz, 5 kHz, 40 kHz"
P11 7.4.2 Analog Dimming Method shows that,
There are descriptions "For example, when the PWM frequency is 5 - kHz, C 5 equal to 1 - μF is sufficient."

From the above, I thought that there was no PWM frequency limit for analog dimming method.

Best Regards,

watanabe

  • 0
    Expert 1740 points
    Hi,

    I have an additional question.

    Datasheet P11 "PWM Dimming Method" has the following description.
    "For example, 2% is the minimum duty cycle for a 200 Hz PWM signal."

    There is no such description in "Analog Dimming Method".
    I recognize that there is no limit of Duty, in the case of Analog dimming.
    Is this a mistake in this recognition?

    There is a brightness you want to achieve with a duty ratio of 0.04%.

    Best Regards,
    Watanabe
  • 0
    TI__Expert 4550 points
    Hi Watanabe,
    Yes, you are right, the frequency 200 to 1000Hz is applied to PWM dimming.
  • 0 in reply to watanabe
    TI__Expert 4550 points
    Hi Watanabe,
    Although there is no description in datasheet about the minimal dimming level, there is current accuracy matter you need to consider. At the maximum dimming level, there around 2.5% tolerance, when you dim down, we can't guratee the accuracy. When you dim down to 0.04% level, it is really low, the output current may not be regulated.
  • 0 in reply to Caryss Li
    Expert 1740 points
    Hi Li,

    I appreciate for your support.

    My customer has new questions.

    Q1.
    What is the recommended frequency for analog dimming?

    Q2.
    It is said that there is a possibility that the output current may not be adjusted with Duty 0.04%,
    Currently, we have confirmed that the duty ratio is the specified duty ratio.
    Is it OK with Duty 0.04%?

    Best Regards,
    Watanabe
  • 0 in reply to watanabe
    TI__Expert 4550 points
    Hi Watanabe,
    A1.
    Above 20kHz would be better, to avoid acoustic noise.

    A2.
    Dimming down to 0.04%, the current regulation could be guaranteed. I don't think we have enough data to predict the current tolerance at that dimming level. If 0.04% dimming is necessary, you may need better device than TPS61500 to provide over 2500:1 dimming ratio. May I ask what is your application here?
  • 0 in reply to Caryss Li
    Expert 1740 points
    Hi Li,
    Thank you for quick reply.

    A1.I understand Above 20kHz would be better.

    A2.The application is a tablet.

    Best Regards,
    watanabe
  • 0 in reply to watanabe
    TI__Expert 4550 points
    Hi Watanbe,
    If you want to use one string application, TPS61197 has 5000:1 dimming ratio.