LC Filter

4.5 LC Filter

The LC filter serves two purposes in this design.

1)Reduces EMI

2)Enables overcurrent (OC) protection.

The outputs of the TAS5111 are square waves with fast rise and fall times. The square waves produce harmonics up to 500 MHz. The speaker wire makes transmission lines for these frequencies. The LC filter attenuates the high frequencies that are transmitted over the speaker wires and increase EMI. The LC filter is shown in Figure 4−9.

Figure 4−9. APA100 Output Filter

TAS51xx

Output A

L

 

 

C1A

 

C2

 

C1B

Output B

L

 

R(Load)

To limit near-field EMI, the loop area of the output switching path through the inductor and capacitor must be minimized. To minimize the far-field EMI, filter each output referenced to a clean ground. Capacitors C1A and C1B filter the outputs referenced to ground. Capacitor C2 adds differential filtering to minimize the loop area. Also, 100-nF capacitors need to be placed from each output terminal (where speaker wires leave the board) to a clean ground. Increasing the capacitors (C1A, C1B, and C2) lowers the cutoff frequency, which improves EMI performance but also increases current flow in the filter. The type of inductor is important for limiting EMI. Multiple winding inductors can be made small, but the multiple windings start to function capacitively at a lower frequency and do not attenuate as much of the 100-MHz to 500-MHz harmonics that are needed to eliminate EMI. For additional EMI suppression, a ferrite bead can be placed in series with the inductors.

The inductor must have 8 ∝H of inductance or more at 15 A, for overcurrent (OC) protection to be effective. The TAS5111 data sheet recommends 5 ∝H of inductance, but that is for a switching frequency of 380 kHz. The APA100 switches at 250 kHz and needs more inductance to protect the device.

The modulation scheme used by the APA100 (based on the TPA2001D1 modulation scheme) can be used without a filter if EMI and OC protection are not important. For more information on the filter−free modulation, see the application section of the TPA2001D1 data sheet.

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Texas Instruments manual LC Filter, 9. APA100 Output Filter
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APA100 specifications

Texas Instruments is known for its innovation in the field of analog and embedded processing, with the APA100 being one of its noteworthy products. The APA100 is an advanced analog front-end (AFE) device designed to meet the needs of various applications including industrial, automotive, medical, and consumer electronics.

One of the standout features of the APA100 is its high-resolution data conversion capability. It integrates both analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), providing unmatched precision and accuracy in signal processing. The device supports multiple sampling rates, which allows it to adapt to various requirements in different applications, ensuring optimal performance.

The power efficiency of the APA100 is another significant characteristic. Designed with low-power consumption in mind, it enables battery-operated devices to maximize their lifespan while maintaining reliable performance. This energy efficiency makes the APA100 suitable for wearables and portable medical devices, where power management is critical.

In addition to its power efficiency, the APA100 features integrated signal conditioning, which includes amplifiers and filters that enhance the quality of the input signals. This capability reduces the need for external components, thereby simplifying system design and reducing overall costs. With its built-in signal conditioning, engineers can expect improved accuracy and reduced noise in their measurements.

Texas Instruments has also included advanced communication interfaces in the APA100, such as SPI and I2C, to facilitate seamless integration with microcontrollers and processors. This flexibility allows for easy implementation into existing systems, enabling developers to take full advantage of the device's features without extensive re-engineering.

The APA100 is also designed for robustness, featuring a wide operating temperature range, making it suitable for use in harsh environments. This reliability is crucial for industrial applications where device performance can be affected by temperature fluctuations.

Overall, the Texas Instruments APA100 is an exceptional analog front-end device that combines high precision, low power consumption, integrated signal conditioning, and robust design. Its versatile features make it an ideal choice for various applications, paving the way for advancements in technology and improved performance across different sectors. With the APA100, engineers have a powerful tool that can help them innovate and enhance their products in highly competitive markets.
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