Texas Instruments APA100 manual 2. Open− and Closed−Loop Frequency Response

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Feedback System Design

operational amplifier (R22, R23, C20, C23, and C24) was eventually reduced from 400 kHz to 252 kHz to optimize performance; compensation for this is discussed later. Notice that in Figure 4−8, the switching frequency of each output is 250 kHz, but the differential frequency is 500 kHz. The poles greater than 400−kHz from the low-pass filters do not affect the stability because they are ten times the corner frequency. The phase from a pole starts at the pole frequency divided by ten. If the pole is ten times greater than the corner frequency, the phase margin is not affected.

Figure 4−2. Open− and Closed−Loop Frequency Response

Open Loop Gain

FP0

 

X

20 dB /

Decade

Gain − dB

Closed Loop Gain

Low Pass

Filters’ Poles

FP0

Fc = 40 kHz X

10

XX

0 Degrees

Phase

FP0* 10

−90 degrees

Frequency − Hz

Figure 4−2 shows what the open−loop gain and closed−loop gain would look like if there were no other poles or delays in the system. The integrator pole causes the open−loop gain to decrease at a rate of 20 dB per decade after the pole and causes the phase to shift by 90 degrees over a span of two decades centered at the pole frequency.

Phase Margin + 180° ) Phase (at Fc)

(1)

From Equation 1, the phase margin of this system is 90_. The device needs 0_ to 180_ phase margin for stability, and most designs require 35_ to 180_. This design would work. However, the TPA2001D1 has an internal feedback loop with an 80-kHz corner frequency, which adds a pole to the system and impedes the stability. The added 80-kHz pole drops the phase margin to 45_, which is still acceptable if there were no other delays.

The added delays decrease phase margin; therefore, more phase margin is needed to ensure stability. A zero is added to cancel the pole, which returns the overall closed−loop frequency response back to the original design. The zero can be created by adding a resistor in series with the integrator feedback resistor. Figure 4−3 shows the effects of the added zero.

Technical Information

4-3

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Contents User’s Guide Important Notice About This Manual Read This FirstRelated Documentation From Texas Instruments Contents Tables FiguresEVM Overview Power Requirements Features2 TPA2001D1 and TLV2464A Supply Voltage 3-V Reference EVM Basic Function/Block Diagram−2. APA100 EVM Block Diagram PCB Design Split Ground Plane PCB LayoutBridge Layout PCB Layers −4. Bottom Copper and Silkscreen Bill of Materials −1. Parts ListSchematic Page EVM Operation Quick Start Power SupplyReset Button/Mute Power−Up/Down SequenceError Signals Changing the Gain Technical Information Feedback System Design −1 shows the block diagram of the feedback loop−2. Open− and Closed−Loop Frequency Response −4. APA100 Integrator Design Feedback System Design −5. Pspice Circuit for Simulating the Feedback −6. Pspice Simulation of Open−Loop Response TPA2001D1 Class-D Modulator−7. TPA2001D1 Block Diagram TAS5111 H-Bridge TLV2464A Gain Setting and Feedback−9. APA100 Output Filter LC Filter−1. TAS5111 Thermal Table ThermalThermal Measured Results −1. APA100 THD+N vs Frequency With 4- W Load Total Harmonic Distortion + Noise−3. APA100 THD+N vs Output Power With 4- W Load −5. APA100 Output Power vs Supply Voltage With 4- W Load Output PowerEfficiency −7. APA100 Efficiency vs Output Power With 4- W LoadSignal-to-Noise Ratio SNR Gain and Phase ResponseSupply 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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