LM5155 is a new generation of boost controller of Texas Instruments, which has the following advantages in the application of pull rod speakers:
Support 3.5-V to 45-V wide range input, applicable to different types of batteries
Built-in 1.5A gate drive circuit can drive high-current MOSFETs, which is suitable for the design of high-power speakers. Compared with other boost schemes on the market, LM5155 can significantly improve efficiency and reduce power consumption, thus extending the battery life of pull rod speakers.
The overall scheme is small in size, simple in design and low in BOM cost:
The chip adopts small size WSON package, only 3mm × 2mm, as shown in Figure 4.
Support high switching frequency (100 kHz to 2.2 MHz), which can effectively reduce the size of external inductance and capacitance and reduce costs.
The working frequency is programmable, and the external clock synchronization is provided, so the EMI design is more flexible
It supports programmable undervoltage protection (UVLO) and soft start, and has perfect overvoltage, overcurrent and thermal protection, providing multiple protection for the whole system.
Figure 5 is a typical application circuit diagram of LM5155.
Figure 4. LM5155 packaging schematic diagram 5 LM5155 boost application circuit diagram
Application of Texas Instruments Audio Power Amplifier in Trolley Speakers
Based on the latest semiconductor manufacturing technology and rich experience in audio power amplifier design, Texas Instruments has launched a series of Class D power amplifier products with excellent performance, high cost performance, and multiple product options, which can meet the needs of different power grade pull rod speakers.
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Power level
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50- 100W
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200- 600W
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Analog input Class D power amplifier
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TPA3128
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TPA3126
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TPA3220
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TPA3221
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TPA3251
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TPA 3255
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Digital input Class D power amplifier
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TAS5825P
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TAS3251
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The power supply voltage (PVDD) of Class D power amplifier is usually provided by boost DC/DC converter in the application of pull rod speaker. Compared with fixed PVDD, variable PVDD adjusted based on the size of audio signal can significantly improve system efficiency, reduce loss, reduce heat, and extend battery life.
TAS5825P is a digital input class D power amplifier chip newly launched by Texas Instruments in 2019. The chip has a powerful audio DSP core built in and implements a proprietary algorithm called Hybrid Pro. Hybrid-Pro algorithm can detect the upcoming audio power demand, and provide PWM control signal for DC/DC converter through the feedback pin (HPFB) to adjust the output voltage (i.e. the power supply voltage PVDD of Class D power amplifier). TAS5825P supports a delay buffer of up to 4ms to view the audio signal in advance and prevent audio clipping distortion.
Figure 6 shows the system block diagram of TAS5825PEVM, an audio power amplifier solution with dynamic voltage regulation realized by LM5155 and TAS5825P. As shown in the figure, the audio signal is processed by the Hybrid-Pro algorithm and fed back to the feedback (FB) end of the boost controller LM5155, so as to realize the envelope detection of the audio signal and control the output voltage of LM5155. The built-in delay buffer of TAS5825P can delay the input of music signals to the power amplifier, thus avoiding the distortion of audio output. As can be seen from the experimental waveform in Figure 7, the power supply voltage PVDD will be adjusted according to the envelope amplitude of the audio input signal and ensure that the audio output is distortion-free.
Figure 6. System block diagram of TAS5825P realizing dynamic voltage regulation audio power amplifier
Figure 7. Experimental waveform of TAS5825P realizing dynamic voltage regulation audio power amplifier
According to the experimental test, 7500mAh single lithium battery supplies 2 × 20W power amplifier is used for power supply. If Class D power amplifier without dynamic voltage regulation is used, the battery life is 2 hours; If the power amplifier is TAS5825P with Hybrid-Pro algorithm, the battery life can be extended to 6 hours, and the battery life is 3 times of the original. For high-power pull rod speakers, the dynamic range of music changes more, and the effect of power saving is particularly significant.
On the official website of Texas Instruments, you can find more solutions for boost power supply and audio power amplifier that are applicable to the application of pull rod speakers.
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