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Audible Noise from BQ500410AEVM-085

Tapan Mittal
Prodigy 40 points

6545.noise1.wav

The attahed file is an audio recording done on my Nexus4 while being charged on a FOD disabled BQ00410A EVM-085 board. The noise is audible and sequenced. It shows up as soon as a Qi device is placed and charging. Even with the BQ51013EVM-725 and MSP430BQ1010, the same noise is audible, although the magnitude might be different by say, 10% and the sequence might be a little different, but not much in any case. (noise present irrespective of FOD setting, FOD was disabled only for Nexus4)

From my observation, the noise is from the PCBA side, and probably from one or more of the components of the particular bridge rectifier circuit that is active (this being an A6 3Coil board).

Could you please help resolve quickly? We are making a transmitter solution and any audible noise is very detrimental to our product. An OEM is also using TI 410A solution and their circuit has the same issue. Maybe it's just a components/boarding/coating issue, but it is serious. Another chipmaker's solution does not have this issue. 

Please help resolve asap.

  • 0
    Prodigy 40 points

    Bill, Any inputs?

    Anyone else notice this?

  • 0 in reply to Tapan Mittal
    Prodigy 10 points

    I get this same noise pattern on a Rx board I built, but it's on the receiver side (happens on a number of chargers). Does it have to do with the resonant capacitors not being the proper values? It's not as audible as that (I would have to put my ear directly next to the Rx board to hear that) but it is obvious from the LED indicator in that it pulses with the pattern. Further, when probing one of the coil inputs to ground, it is noticeable on a scope.

  • 0 in reply to Ashley Miller1
    TI__Guru* 75866 points

    Acoustic noise from ceramic capacitors is common on electronic equipment.  Several articles have been written on how to reduce the noise.  Problem is not unique to wireless power and solution used on other systems will work here.

    The root cause of the noise is piezoelectric characteristics of mult layer ceramic capacitors, voltage changes on the capacitor cause physical changes.  This result is capacitor flexing the PCB which acts as a speaker diaphragm.

    Type II capacitors such as X7R and X5R will show this problem.  Type I capacitors such as COG and NPO do not have this issue.

    In the wireless power application the voltage change on the capacitor is coming from the communications packets, typical sent every 250mS. 

    On the RX side (bq510XXX) voltage change will show up on the capacitor connected to the VREC pin, filter caps for unregulated voltage.

    On the TX side (bq500XXX) voltage change will show up on the bulk input filter caps between Vin and the power section.

     

    Possible solutions:

    1.)    Splitting capacitor into mult smaller devices, replace one large cap with 3 or more smaller capacitors. Mechanical force on the board is reduced.

    2.)    Placing capacitors on both sides of the board, top and bottom.  The force is balanced between the top and bottom capacitor and PCB does not flex.

    3.)    Adding slot to the PCB to decouple the force from PCB.

    4.)    Use Type 1 MLCC or Tantalum capacitors.

    5.)    Use Murat low noise GJ8 or KRM series capacitors

    6.)    Use AVX QM series capacitors

     

    Ref Article:

    1.)    Reduce Acoustic Noise from Capacitors—Damian Bonicatto—EDN Feb 17, 2011

    www.edn.com/design/components-and-packaging/4364020/Reduce-acoustic-noise-from-capacitors

     

    2.)    Examples of Noise Countermeasures, Murat Manufacturing – Online Training.

    www.murata.com/products/capacitor/solution/naki.html

     

    3.)    Kyocera (AVX) Reduced Noise QM Series---Digikey Online Training –

    http//dkc1.digikey.com/il/en/tod/AVX/Reduced-Noise-QM-Series/Reduced-Noise-QM-Series.html