App note: How to properly configure unused operational amplifiers


Good read app note from Texas Instruments about configuring unused op amps on multi amp chips. Link here (PDF)

Multi-channel operational amplifiers (op amps) are often implemented in circuits that do not require the use of all channels. Undesired behavior in an unused amplifier channel can negatively impact system performance, as well as the performance of the channels in use. To avoid degradation of both the op amp and system performance, the unused op amp channels must be configured properly.

App note: Current sense amplifiers in class-D audio subsystems


App note from Texas Instruments about output current sensing in class-D amplfiers. Link here (PDF)

Current sensing in audio subsystems are widely used in conjunction with CLASS-D amplifiers for diagnostics or to provide speaker current feedback to the DSP for speaker enhancement to emulate smartamp. The most expensive component in the audio subsystem is the speaker. The impedance of the speakers ranges from 2Ω for subwoofer to a 8Ω for stereo speakers. Exceeding the current flowing through the speakers has a potential to create excessive heat in the voice coil which can lead to permanent damage of the speakers.

App note: Implementation of a single-phase electronic watt-hour meter using the MSP430AFE2xx


Another energy meter from Texas Instruments using MSP430AFE2xx. Link here (PDF)

This application report describes the implementation of a single-phase electronic electricity meter using the Texas Instruments MSP430AFE2xx metering processors. It includes the necessary information with regard to metrology software and hardware procedures for this single chip implementation.

App note: Extend current transformer range


Design note from Texas Instruments on technique in resetting and negative voltage generation from current transformers. Link here (PDF)

Transformers are used extensively for current sensing because they can monitor currents with very low power loss and they have wide bandwidth for good waveform fidelity. Current transformers perform well in applications with symmetrical AC currents such as push-pull or full bridge converter topologies. In single-ended applications, especially boost converters, problems can arise because of the need to accurately reproduce high duty factor, unipolar, waveforms. Unipolar pulses may saturate the current transformer and, if this happens, overcurrent protection will be lost and, for current mode control, regulation will be lost and an over voltage condition will result.

App note: Understanding undervoltage lockout in display power devices


Texas Instrument’s application note about how undervoltage lockout (UVLO) protect devices from undefined behavior. Link here (PDF)

Many integrated circuits include an undervoltage lockout (UVLO) function to disable the device at low supply voltages. Below the minimum supply voltage the function and performance of a device may be undefined, making it impossible to predict system behavior. This application note explains how to correctly understand the undervoltage lockout specification in the data sheets of TI’s Display Power products.

App note: Load switches: What are they, why do you need them and how do you choose the right one?


Application report from Texas Instruments on load switches to simplify power supply design. Link here (PDF)

Integrated load switches are electronic relays that can be used to turn on and turn off power supply rails in systems. Load switches offer many other benefits to the system and can include protection features that are often difficult to implement with discrete components. There are many different applications where load switches can be used including, but not limited to:

-Power Distribution
-Power Sequencing and Power State Transition
-Reduced Leakage Current in Standby Mode
-Inrush Current Control
-Controlled Power down

This application note will provide the fundamental basics of what load switches are, when they should be used, and how they can be implemented in a system.

App note: Low-power battery temperature monitoring


Low current consumption temperature battery monitoring TMP303 from Texas Instruments. Link here (PDF)

Charging a battery cannot be independent of temperature. In fact, most batteries specify a range of temperatures where charging is permitted. Charging outside these bounds risks damage, failure or worse. To prevent charging when the temperature is too hot or too cold, a temperature sensor and corresponding circuitry are required to disable the charging circuit accordingly. Some temperature sensors like TMP303 already incorporate this functionality. TMP303 monitors the local temperature and asserts its output when the temperature rises above or falls below factory-programmed trip points. This output signal is used to disable the charging circuit.

App note: Stopping reverse current flow in standard hot swap applications


Application report from Texas Instruments about a simple circuit that blocks reverse currents. Link here (PDF)

The proposed circuit uses an inexpensive operational amplifier to sense the condition of the output voltage exceeding the input voltage, and subsequently disable the hot swap controller, stopping the flow of reverse current (current flow from the output (load) into the input (supply)). The device used for testing this method is the LM5069, configured to provide hot swap control of input voltages from 11V to 22V to a load capacitor of 220 µF. A schematic of the solution and results are provided.

App note: Noise analysis for high-speed op amps


An application report on op-amp noise analysis from Texas Instruments. Link here (PDF)

As system bandwidths have increased, an accurate estimate of the noise contribution for each element in the signal channel has become increasingly important. Many designers are not, however, particularly comfortable with the calculations required to predict the total noise for an op amp, or in the conversions between the different descriptions of noise. Considerable inconsistency between manufacturers in describing noise and, in some cases, incomplete specifications, have contributed to this confusion. A thorough description of the op amp noise model will be developed here with a detailed discussion of the key differences between current and voltage feedback amplifiers. The conversions between several different measures for noise used in the industry will also be described. Broadband effects will be covered for both low frequencies (the 1/f region) and high frequencies (noise power bandwidth).