TA2022 and TAS5010 digital power amplifier circuit diagram

Digital power amplifier is a new type of device, and IC manufacturers will naturally not let go of this business opportunity and have launched unique digital power amplifier products one after another. Below is a brief introduction to some representative devices.

The TA2022 is an analog input stereo integrated modulator and output stage produced by Tripath. What makes it unique is that its modulator uses a spread-spectrum switching pattern rather than a fixed frequency, hence the company's designation as a "Class T" amplifier. The device can output 25W of power per channel into an 8Ω load at ±25V supply voltage, with idle power loss measured at 3.4W. TA2022 has 0.015% THD at 25W; rising to 0.1% at 60W. It is packaged in an SSIP-32 plastic package and requires an external heat sink.

The Cirrus Logic CS4421) is a Class D controller that is used with a pair of IR Corporation's IRCS8001 bridge drivers. 4421O can have 3 serial digital audio inputs, built-in multi-channel switch and main interface, and is packaged in TSSOT-24. The IRCS8001 bridge drivers are packaged in SOIC-16, each driving 4 IRC8101 MOSFET full-bridge structures, or 2 IRC8102 MOSFET half-bridge structures, achieving 50W of power on an 8Ω speaker. The amplifier THD is 0.01% at 1KH z, 1W; it is 0.1% at full power. This amplifier combination can achieve good stereo effect.

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Direct Digital Amplification (DDX) is an application-specific integrated circuit developed by Apoget Technolog and licensed by STMicroelectronics. The device combines Apogee sub-micron CMOS technology and ST bipolar-CMOS- DM OS (BCD) technology. The hybrid process makes it possible to manufacture CMOS devices and power DMOS devices on the same chip. DDX's damped three-state PWM scheme further improves efficiency. The efficiency of a typical DDX amplifier is 20% higher than that of a Class D amplifier and 300% of that of the Class AB amplifier class. On-chip control processing functions perform basic DDX modulation as well as other DSP-based signal processing functions for surround, tone and volume control. Currently commercialized devices include the STA304A controller and two power amplifiers; STA500 (2×30W) and STA505 (2×50W). The STA304A converts two serial digital inputs in IIS or S/PDIF format into digital signals that drive a 5-channel power amplifier, and the embedded software adds other functions such as equalization. Due to the extremely high chip efficiency, STA500 is assembled in Power S036, which has the advantages of surface mounting and power capacity.

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TI's true digital power amplifier (TDAA) consists of the TAS5010 PCM-PWM modulator and the TAS5100 digital power amplifier. The system accepts the serial PCM digital audio stream and converts it into a 3.3V PWM audio stream, then amplifies it into a large signal PWM, and then demodulates it to drive the speaker. T AS50 10 is an innovative, high-performance, economical and practical 24-bit stereo PCM-PWM modulator based on Equibit technology. The device offers a choice of serial input formats including left-justified, right-justified, IIS or DSP data formats, is fully compatible with the AES standard sample rate, and provides de-emphasis functionality. There is also a digital interpolation filter inside the 5010, which upsamples the audio data to 352.8KHz or 384KHz at 2x, 4x, or 8x (depending on the sampling rate). This rate is the TDAA internal sampling rate. The Equibit modulator converts the upsampled signal into a PWM signal of the same frequency. The modulator uses a complete patented correction algorithm to compensate for nonlinearity and improve the overall performance of the system. TAS5100 is a single-channel PWM power audio device. It consists of an integrated gate driver, four matched and electrically isolated enhanced N-channel power DM OS transistors, and a built-in protection circuit and fault notification circuit. The dynamic range of the TDAA system composed of the above two devices is greater than 93dB; TDH is less than 0.08% (1KHz, 6Ω load, 1W~30W RMS); the power efficiency on the 8Ω load is greater than 90%.

Digital power amplifier practical skills

Although Class D amplifiers have many advantages, they also have some inherent problems that must be dealt with correctly in actual use. Please do not forget the basic fact that D0 operates in pulses in the amplifier and is more sensitive to power supply quality. The power supply should not produce ringing waveforms or voltage changes when delivering rapidly changing current. This requires the energy storage capacitor to have an extremely low effective series resistance (esr), because any parasitic resistance or inductance will prevent the stored charge from transferring quickly. Putting a small low esr capacitor in parallel with the electrolytic capacitor will not help either, because the output power is suddenly transferred in a short period of time and all parallel capacitors are required to have extremely low esr. Using a switching power supply may be the most effective way to solve the problem. This type of power supply usually works at a higher frequency and has a fast built-in load. It does not require a post-wired voltage regulator. The high frequency helps to reduce the energy storage capacitance. Not only that, the efficiency of the switching power supply is higher than that of the linear power supply and can Reduce cooling requirements.

Another common problem with Class D amplifiers is electromagnetic interference (EMI). All PCD copper traces and cables connected to the output stage carry high-frequency high currents and act like an antenna. The easiest way to reduce EMI is to keep these connections as short as possible. If possible, the power supply and output stage should be placed on the same PCB. Speakers are even more difficult to deal with. If the system has built-in speakers, short speaker cables are an effective way to overcome EMI and reduce costs. If the speaker is external and the cable length is beyond the designer's control, a low-pass filter on the output stage is essential.

Low-pass filters will bring another trade-off consideration. The low cut-off frequency not only suppresses EMI, but also attenuates the high-end components of the audio band. High-order filters can meet the above requirements, but the cost is too high and unacceptable, especially for filtering. The inductor must have a high-quality iron core to avoid electromagnetic saturation. Digital speaker equalizers offer a solution. When it is programmed as a triplet boost, it is possible to use a low-order reconfigurable filter with a low cutoff frequency and still maintain a flat frequency response in the audio range. For a PWM signal with a rate of 384KHz, in order to prevent triple tone attenuation, the filter cutoff frequency needs to be approximately 45KHz. For EQ triple boost, the cutoff frequency can be as low as 30KHz. EMI can be reduced by 7dB.