{"list":[{"articleid":"1716","classid":"61","title":"Analysis and Optimization Strategies for MLCC Squealing Issues in Laptops","entitle":null,"author":"admin","comefrom":"","smallpic":"\/static\/upload\/img\/20260303\/1772525389367474.jpg","bigpic":"","keywords":"","description":"","details":"

Traditional electronic devices used many tantalum and aluminum electrolytic capacitors. However, in recent years, due to requirements for product miniaturization and improved reliability, these have been gradually replaced by ceramic capacitors. With the advancement towards multi-functional and quieter electronic devices, the "squealing" (acoustic noise) generated by previously unremarkable ceramic capacitors in power supply circuits of devices like laptops, smartphones, car navigation systems, and wireless chargers has become a significant design concern.<\/span><\/p>

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In laptops, the "squealing" generated by ceramic capacitors used on power lines can sometimes become problematic. When the operating mode changes, such as entering sleep mode or displaying a standby screen, the internal operations of the laptop change. Consequently, the volume of the "squealing" varies according to the operating mode, and the perceived experience differs.<\/span><\/p>

This article introduces countermeasures, evaluation methods, and the generation mechanism of "squealing" caused by capacitors on laptop power lines.<\/span><\/p>

Laptop "Squealing"<\/span><\/b><\/p>

The following three operating modes in laptops are common situations where "squealing" is likely to occur:<\/span><\/p>

  1. Sleep Mode (Buck      Converter: PFM Mode)<\/span><\/b><\/li>
  2. LCD Backlight (Boost      Converter: PWM Dimming)<\/span><\/b><\/li>
  3. Camera Mode \/ Heavy Load      Mode (Intermittent Operation)<\/span><\/b><\/li><\/ol>

    Where are the capacitors prone to "squealing" located in a laptop?<\/span><\/b>
    Capacitors are frequently used on the power lines (primary side of DC-DC converters) in laptops. When ceramic capacitors are used on these power lines, squealing can sometimes occur.<\/span><\/p>

    \"3d4c14e5-aba7-441e-9c4c-2d5d33eecc87.png\"\/<\/p>

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    Simplified Diagram of Laptop Power Lines (Schematic)<\/span><\/b><\/p>

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    \"23e98a10-f121-4366-9a2e-a554e2ce0ae6.png\"\/<\/p>

    (Diagram description: Power input -> DC-DC Converter -> Power line with multiple capacitors -> Various loads like CPU, Camera, RF Module, LCD)<\/i><\/span><\/p>

    Generally, capacitors prone to generating "squealing" exhibit the following characteristics:<\/span><\/p>

    1. Large Capacitor Size.<\/span><\/b><\/li>
    2. Large Capacitance Value.<\/span><\/b><\/li>
    3. High Line Voltage and      Large Voltage (Current) Fluctuations.<\/span><\/b><\/li>
    4. Multiple ceramic      capacitors matching the above criteria are installed on the same line.<\/span><\/b><\/li><\/ol>

      In summary, the reasons why capacitors on laptop power lines are prone to generating "squealing" are:<\/span><\/p>

      1. Power line voltage is      relatively high, typically 10-20V.<\/span><\/b><\/li>
      2. Voltage fluctuations      easily occur to supply power to various circuits like the CPU, camera, and      RF modules.<\/span><\/b><\/li>
      3. If the component      size\/capacitance is large, the dielectric expansion\/contraction due to      applied voltage also becomes larger.<\/span><\/b><\/li><\/ol>

        Squealing Generation Mechanism<\/span><\/b><\/p>

        Why do multilayer ceramic capacitors generate "squealing"? The generation mechanism and Murata's evaluation methods for squealing are explained below.<\/span><\/p>

        \"3c7a5e98-a8df-4b21-909d-b135ec331ef1.png\"<\/p>

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        \"838a9524-d6b9-4a89-b6c0-fd0aa55d0757.png\"<\/p>

        \"50446caf-2cd0-4a58-a146-b93cd7eb0a64.png\"<\/p>

        Mechanism of Squealing Generation<\/span><\/b>
        Ferroelectric materials used in multilayer ceramic capacitors possess piezoelectric properties. When an electric field is applied, distortion occurs. The expansion and contraction of the chip generate "squealing".<\/span><\/p>

        Effectiveness of Squealing Countermeasures<\/span><\/b>
        An example of the effectiveness of squealing countermeasures related to sleep mode\/standby screen\u2014operating modes prone to squealing and exhibiting high sound pressure levels in laptops.<\/span><\/p>

        Effectiveness on Power Line Capacitors<\/span><\/b>
        If squealing occurs when using ceramic capacitors on a power line, applying squealing countermeasures to the offending capacitors can reduce the sound pressure level. The effect comparison is shown above. Of course, the first step in addressing squealing issues is to evaluate the circuit's acoustic noise.<\/span><\/p>

        Evaluation of Squealing<\/span><\/b>
        The main methods for evaluating squealing are the following two:<\/span><\/p>

        1. Sound Pressure Level      Measurement<\/span><\/b><\/li>
        2. Voltage Fluctuation      Measurement<\/span><\/b><\/li><\/ol>

          Since "sound" is the problem, "sound pressure level" is the primary measurement target. The device under test is operated inside an anechoic chamber, and the sound pressure level is measured using a microphone and a sound level meter. Additionally, for evaluation and countermeasure purposes, the frequency characteristics of the sound pressure level are confirmed using an FFT analyzer.<\/span> <\/p>

          Sound Pressure Level Measurement<\/span><\/b>
          To identify the capacitor generating the squealing, we can also measure "voltage fluctuation." While the device under test is operating, we check whether a ripple voltage within the audible frequency range (20Hz to 20kHz) is applied to the capacitor.<\/span><\/p>

          \"50d84826-4922-424d-81db-447d919d90c1.png\"\/<\/p>

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          Voltage Fluctuation Measurement<\/span><\/b><\/p>

          What is the relationship between sound pressure level and voltage fluctuation?<\/span><\/b>
          If the spectrum of the voltage fluctuation applied to a capacitor becomes high at the same frequency as the frequency characteristics of the sound pressure level (indicated by the red dashed box in the figure below), it can be determined that this capacitor is the cause of the squealing.<\/span><\/p>

          \"86274949-8100-485d-880c-41d5d4d65686.png\"\/<\/p>

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          Relationship between Sound Pressure Level and Voltage Fluctuation<\/span><\/b><\/p>

          \"6bf28cc0-5430-4929-a0f6-be4508abcf07.png\"<\/p>

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          Case Study: Laptop Power Line<\/span><\/b>
          When the laptop's operating mode is changed to sleep mode or standby screen, the internal operations change, and consequently, the sound pressure level and voltage fluctuation also change. Since the sound pressure level differs depending on the operating mode, it is necessary to evaluate both the mode where squealing occurs and the modes where it is likely to occur separately.<\/span><\/p>

          \"f04b5b20-fa84-4f55-a092-a5646777740a.png\"\/<\/p>

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          Sound Pressure Level Varies with Operating Mode<\/span><\/b><\/p>

          The figure below shows a simplified circuit diagram of the capacitors targeted for squealing countermeasures on a power line. The pink box indicates the capacitors on the power line that are prone to generating squealing and are the subjects of the countermeasures.<\/span><\/p>

          \"21f107ff-9db2-4449-b523-105ff97efe85.png\"\/<\/p>

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          Capacitors Targeted for Squealing Countermeasures on Power Line (Simplified Circuit Diagram)<\/span><\/b>
          Before branching out to individual circuits via the DC-DC converter, these capacitors are on the same power line and experience nearly identical voltage fluctuations. Therefore, it is necessary to apply squealing countermeasures to all capacitors on this specific power line.<\/span><\/p>

          The countermeasure for power line squealing is not to replace some capacitors but to replace all capacitors on that line with anti-squealing products. This approach can further reduce the sound pressure level.<\/span><\/p>

          Following the circuit order [A \u2192 B \u2192 C], general-purpose capacitors are sequentially replaced with anti-squealing products.
          The sound pressure level gradually decreases as the number of capacitors replaced with anti-squealing products increases.<\/span><\/p>

          Replacement Evaluation:<\/span><\/b>
          The capacitor products used in this evaluation are the following two Murata MLCCs:<\/span><\/p>