One of the core selling points of portable electronic products is the endurance. No matter how the trend changes, the endurance is the same selling point. Especially at present, the battery cost has increased significantly. How to balance the battery life and cost is the focus of product definition.
In addition to the battery cell, my point of view: to extend the endurance is to reduce the calorific value. The key of PCB is to focus on power chips and thermal devices. Take Bluetooth audio as an example. The two chips that generate the most heat, DC-DC boost and audio power amplifier, can not only greatly increase the endurance but also reduce the heat as long as the efficiency of these two chips is improved. These two chips complement each other and circulate in a positive direction.
This article focuses on the significant role of CLASS H. CLASS H is to dynamically adjust the pressure rise according to the music signal. The traditional way is to boost the DCDC to a fixed voltage, such as 15V. When the battery voltage is increased to 15V, the pressure of the boost chip will be relatively large, just like stepping. The greater the step, the greater the pressure, the greater the efficiency will be, and the heat generated will be greatly increased. This traditional fixed boost scheme makes the DCDC pressure not released. No matter how small the average amplitude of the music signal is, the boost chip must maintain a low efficiency state, and the heat generation cannot be reduced.
The audio power amplifier is also facing the same challenge. In the traditional scheme, the power supply of the power amplifier is fixed high voltage regardless of the size of the music signal, and the high level of the output PWM waveform is high voltage. Similarly, the power supply efficiency of 1W, 9V and 18V is quite different.
The function of CLASS H will replace this fixed boost scheme, which will become the trend of a new generation of portable products. The following figure shows the changes of PVDD under the CLASS H function of ACM3108. The following figure shows the PVDD of DCDC in blue, and the audio output signal in green.
With the change of music signal, PVDD can adjust in real time, and leave a certain margin to ensure the sound quality. Both ACM3108/ACM3128 have ClassH function. This function can control the FB pin of the DCDC boost chip through pin 13, thus controlling the DCDC voltage.
Dynamic boost can not only ensure the dynamic range of transient high power, but also reduce the power consumption of the whole machine, which is an ideal comprehensive scheme.
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