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TPS61193-Q1: Audible Noise from Inductor

Balakrishnan K
Prodigy 50 points
Part Number: TPS61193-Q1

Hi 

We are using TPS61193 part in one of design for Gauge illumination and TFT backlight section.

Hearing Audible noise in below ranges: 

Gauge illumination inductor from VIN - 13.2V to 13.6V (Non-Shielded type inductor)

TFT illumination backlight inductor from VIN - 16.5V to 16.8V,  (Using Shielded type Inductor)

Design operating range is Vin = 6V to 18V. 

Findings:

1. Below is schematic image, used 1 x 47uF(electrolyte Cap) & 2 x 10uF(Ceramic Cap) and I changed the ceramic cap (C911 & C912) to 22uF and still hear audible noise. 

2. I removed the  2x10uF(Ceramic cap) and audible noise is completely reduced, But TPS61193-Q1 datasheet recommend to use Ceramic cap in Note A and whereas in Note B recommend to use physical size ceramic cap should be minimized. 

Query: 

1. What will impact if i remove the ceramic cap ?. Since product in final stage and not in place to change the inductor to shielded type from Non-shielded type

2. Without removing capacitor, what would be TI recommendation to isolate the audible noise. 

 

Note A:

Note B:

Thanks and Regards

Balakrishnan

  • 0
    Prodigy 40 points

    I would like to add one more point. During the voltage range where we hear acoustic sound , the Inductor ripple current has audible frequency range (6KHz till 25KHz). I feel this is the reason for making audible noise from Inductor in the circuit. But, we need the ideas/solution to avoid the ripple current to fall in the audible frequency range. I have attached the TFT Backlight power supply circuit for your reference. 

    Input Operating voltage level = 6V to 18V.

  • 0 in reply to Srikanth Goud
    TI__Expert 5475 points
    Hi,

    Could you please send me your SW node waveform or inductor current waveform? It seems the boost has entered the pulse skip mode. For the schematic, a problem I can see is the inductor value. The switching frequency is 1.9MHz. In that case, the recommended inductance is 4.7uH or 10uH. 22uH is a little bit high.
  • 0 in reply to Shirley He
    Prodigy 40 points

    Hi, Please find the SW node switching waveform (Yellow) & Inductor ripple current (Blue). Let me know if you need any other info.

    FYI: I tried changing the Inductor values to 4.7uH as well as 10uH. But the accoustic sound is still existing.

    BR/Srikanth

  • 0 in reply to Srikanth Goud
    TI__Expert 5475 points
    Hi,

    It can be seen from the waveform that the input voltage is very close to the output voltage. In that case it is inevitable that the boost will work in pulse skip mode and there may be audible noise. Is this your typical working condition that the input voltage is very close to the output voltage?
  • 0 in reply to Shirley He
    Prodigy 40 points
    Yes, It is expected to operate within 6V to 18V. Typical operating point is at 13.5V, but clusters will run from external battery , where we do not have control. So, It is a concern for us to hear that sound in the circuit. Do you have any other alternative ideas to avoid the IC to switch out of audible range? We are using Shielded Inductor type.
  • 0 in reply to Srikanth Goud
    Prodigy 40 points

    Hi Team,

    Can you please support us on this issue with priority?

    BR/Srikanth

  • 0 in reply to Srikanth Goud
    TI__Expert 5475 points
    Hi,

    When the input voltage is infinitely approaching the output voltage, there will definitely be some point where the pulse skip frequency enters the audible frequency range. This is not very common use case because the output voltage is usually some volts higher than the input. One way you can try is to add resistor in series with the LED to increase the output voltage.