Texas Instruments APA100 Feedback System Design, 1 shows the block diagram of the feedback loop

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Feedback System Design

4.1 Feedback System Design

The APA100 EVM uses feedback to lower distortion, increase supply ripple rejection, and make the gain not change with supply voltage. This section goes through the following steps to close the loop.

1)Take feedback at TAS5111 outputs before the LC filter, so that it is unnec- cary to cancel two poles of the LC filter.

2)Set corner, Fc, frequency to less than half the minimum switching frequen- cy, Fsw.

3)Add filtering at frequencies greater than 10 times the corner frequency.

4)Add a zero to the integrator to cancel TPA2001D1 pole.

5)Calculate the open−loop gain and set closed−loop gain.

6)Design circuit / component selection.

7)Simulate and adjust.

Figure 4−1 shows the block diagram of the feedback loop.

Figure 4−1. APA100 Block Diagram

Sum and

Integrate

AudioGain

Output

− 33 dB

Differential to Single -

Ended Converter

 

Analog Input

 

H-Bridge

 

 

 

Class-D

 

 

Modulator

 

(TAS5111)

 

 

 

TPA2001D1

 

 

 

 

 

 

 

 

 

 

Gain = 18 dB

 

Gain = A+/3 V

Audio Output

The feedback is taken at the TAS5111 outputs before the LC filter. If the feedback were taken after the LC filter, the two poles caused by the second−order, low−pass filter would have to be cancelled with zeros in the integrator. This is difficult and would limit the inductor and capacitor to a tight tolerance.

When closing the loop, the first thing to choose is the corner frequency. For a class−D amplifier, the closed−loop corner frequency needs to be less than half the minimum switching frequency. The minimum switching frequency of the TPA2001D1 is 200 kHz, limiting the maximum corner frequency to 100 kHz.

An 80-kHz corner frequency was originally designed, but the switching waveform input to the TPA2001D1 added noise and distortion. Therefore, the corner frequency was lowered to 40 kHz, and low-pass filters set at 400 kHz were added in the feedback to reduce the 500-kHz differential signal that is input to the TPA2001D1. The cutoff frequency of the filter before the

4-2

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Contents User’s Guide Important Notice Read This First About This ManualRelated Documentation From Texas Instruments Contents Figures TablesEVM Overview Features Power RequirementsEVM Basic Function/Block Diagram 2 TPA2001D1 and TLV2464A Supply Voltage 3-V Reference−2. APA100 EVM Block Diagram PCB Design PCB Layout Split Ground PlaneBridge Layout PCB Layers −4. Bottom Copper and Silkscreen −1. Parts List Bill of MaterialsSchematic Page EVM Operation Power Supply Quick StartPower−Up/Down Sequence Reset Button/MuteError Signals Changing the Gain Technical Information −1 shows the block diagram of the feedback loop Feedback System Design−2. Open− and Closed−Loop Frequency Response −4. APA100 Integrator Design Feedback System Design −5. Pspice Circuit for Simulating the Feedback TPA2001D1 Class-D Modulator −6. Pspice Simulation of Open−Loop Response−7. TPA2001D1 Block Diagram TLV2464A Gain Setting and Feedback TAS5111 H-BridgeLC Filter −9. APA100 Output FilterThermal −1. TAS5111 Thermal TableThermal Measured Results Total Harmonic Distortion + Noise −1. APA100 THD+N vs Frequency With 4- W Load−3. APA100 THD+N vs Output Power With 4- W Load Output Power −5. APA100 Output Power vs Supply Voltage With 4- W Load−7. APA100 Efficiency vs Output Power With 4- W Load EfficiencyGain and Phase Response Signal-to-Noise Ratio SNRSupply Ripple Rejection

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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