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Original question:

TPS61199: The relation between OVP and LED bar Vf

TPS61199: The effect of different output capacitor materials on output ripple.

Kami Huang60
Genius 3830 points
Part Number: TPS61199

Dear Sir/Ms.

Customers use TPS61199 to design Back light LED Driver. After the experiment, it was found that sound was generated, and the output capacitance was found to have an effect.
TPS61199 Vin is 12V
                        Panel Specifications
                        LED String Current 70mA (Typ.) 77mA (Max.) Note: 4 strings and 7pcs LED of one string
                        LED String Voltage 19.6V (Min.) 21.7V (Typ.) 23.8V (Max.)
The customer's product issue has been resolved.
But the manager of RD wants to know why this is happening? The customer has removed the E-CAP, the MLCC has increased the test, and still has a voice. Is there any hat can explain the difference between E-CAP and MLCC as output capacitors?

Attached is experimental data.

Best Regards,

Kami Huang

TPS61199 test 012020.doc

  • 0
    TI__Mastermind 22745 points

    Hi Kami,

         That's the normal phenomenon since you are using PWM dimming, the output current will follow the input PWM signal so it is also PWM shape, this will lead to a large output voltage ripple. And the dimming frequency is below 20kHZ which will lead to the audio noise. So for such PWM dimming application, we strongly recommend using an E-CAP with MLCC-cap together.

    Regards

    Sean