【 ShenMao school 】 Reveal the cause of capacitance squealing

减少小电容的esr及esl,会员考虑减少小电源上的纹波及噪音,续电源模组的小型化辨析趋势,所以影片式多层陶瓷电容mlcc ( 多层陶瓷电容器) Is increasingly used in the output capacitance. 学习日语使用mlcc电容会产生一个新问题,但不少会导致啸叫。 啸叫mlcc电容陶瓷的强介电性会诱发压电效应,叠层电容在施加交流电之后,会在叠层方向( z轴) 发生舒张。 因采收介电体的泊松比( Poisson ratio) 一般使用者。 3, so with laminated direction ( z轴) The vertical direction ( x与y轴) , i. e. , parallel to the circuit board can also occur in the direction of the scale, as a result, the circuit board surface vibration and can hear the sound. Although the capacitor and the amplitude of circuit board is only 1 PM ~ 1 nm, but vibration has been large enough to we can hear voice, will hear the sound of the similar 'ji'. Terms: poisson's ratio is refers to the material in a one-way tensile or compressive, transverse normal strain and axial strain is the ratio of the absolute value of, also called the poisson ratio, it reflects the elastic constants of the lateral deformation of the material. 所以,电容性时啸叫实上是电容压电效应导致了pcb的形可。 Therefore, inhibition of capacitance noise are the main measures of inhibition or offset PCB deformation. For example, can cause the noise of the capacitance on the same side, placed at different angles. Or on both sides, it is to put; Also, can choose the capacitor with stents, of course, it would increase costs, as shown in figure 3. Above by inhibiting the PCB deformation way to deal with the problem capacitance squealing take temporary solution not effect a permanent cure, as far as possible to get rid of the causes of noise from the source. In fact, the capacitance caused by the noise of the reason is very simple, must be loaded on the capacitor is the human ear can hear an alternating current ( 此时率为20 hz ~ 20 khz) 。 Therefore, the analysis of the basic idea is as follows: first, roughly search capacitance is screaming with ears that an area; Then, using the oscilloscope screen suspicious voltage signal, as shown in figure 4 lists some once capacitance caused by the noise voltage signal, for your reference. # 18. 4 khz # # 6。 3千赫# # 4。 # 3 KHZ, light load model in figure 4. Once capacitance caused by the noise voltage signal by summing up the related case, capacitance of the noise is most happened in light load mode. According to its reason, because the chip in light load mode usually into efficient mode. 小编效模仪式,系统处于半开环模式,晶片监控次馈电压但是不开采应立即次,只有当出口电压低于阈值时,岁会发送几枚pwm脉冲,往电感和出口电容一点点末充上电。 制作5是轻载模式下的开关节点v姐信号。 Figure 5. 轻载模式下的开关节点信号在轻载模式下,出口电压的纹波电压会比较大,该时代过度电容性交流电力宽带率也比较离散,所以容易发生啸叫事件。 为了轻载模式的本意是良性的,降低了系统化的静语态电流。 当系统处在deep sleep模式,一般只有少数几路常电在以极低的负载电流( As two hundred microamps) At work, so that the energy generally is not enough to cause capacitance of the noise. However, if the light load model ( 睡眠模式) With Normal PWM mode ( 正常运行模式) 切换的阈值没有被恰当地设置的故事,系统可能会在负载电流比较小的时候骏滞留在轻载模式而无法切入normal pwm模式,这样性后果是离散开关脉冲也许会引啸叫起电容。 关于轻载模式和强制pwm模式设置的一般建议了:1、一级电源并且是常电模式,建议软体参与控制。 设置在系统进入休眠之前,由软体晶片进入轻载模式; 当系统从休眠模式,被唤醒软体需求及时地将电源设置为强制pwm模式。 2、中文二级电源并且对轻载效率的要求不是特别严苛时,尽量全程设置为强制pwm模式。 There are some circuit especially the low cost of simple circuit, software have no way to set the PWM mode, unfortunately capacitance mega event happened again, can try the following methods: 1, change the value of capacitance, even try different manufacturers or different types of capacitors; 2、安装假负载 小阻值的电阻作为假负载) , this is no way; 3, 'redundant' capacitance can also cause the loop is not stable, lead to the noise, can try to remove some 'nice-to-have' capacitance; 4、夸大的出口电容会导致相位裕量过大,这会延缓pwm模式的时机,进入尝试适当减小相位裕量。
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