App note: Minimizing light flicker in LED lighting applications

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Another application notes from Richtek this time on LED lamps flickering. Link here

Applying LEDs in offline retrofit lamps seems straightforward, but should be done with care to achieve similar light quality as the conventional lamp that the user is trying to replace. Light flicker is one of the aspects that need to be considered carefully during LED lamp design to avoid customer complaints from the field. This application note explains the LED lamp flicker phenomena in relation to driver topology and LED characteristics, and provides solutions based on several Richtek LED drivers in combination with specific LED strings. A practical flicker measurement method is explained as well, that can be used to measure light flicker in LED lamps.

App note: Li-ion battery and gauge introduction

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Richtek app note for Li-ion battery definitions and gauge introduction. Link here

SOC is defined as the status of available energy in the battery and usually expressed as percentages. Because the available energy change depends on different charging/discharging currents, temperatures and aging effects, the SOC could be defined more clearly as ASOC (Absolute State-Of-Charge) and RSOC (Relative State-Of-Charge). Typically, the range of RSOC is from 0% to 100%, a fully charged battery’s RSOC is always 100% and a fully discharged battery has 0% RSOC. The ASOC is a reference calculated by Design Capacity which is a fixed capacity from when the battery is manufactured. A fully charged new battery will have 100% ASOC, but a fully charged aging battery could be less than 100% because of different charge/discharge conditions.

Battery management is part of power measurement. The fuel gauge is responsible to estimate the capacity of battery in the domain of battery management. The basic function of fuel gauge is to monitor the voltage, charge/discharge current and battery temperature, and to estimate the battery’s SOC and Full Charge Capacity (FCC) of battery. There are two classic methods to do the SOC estimation which are Open Circuit Voltage (OCV) and Coulomb Counter, respectively. The other method is dynamic voltage-based algorithm designed by RICHTEK.

App note: LED diagnosis in automotive applications

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App note from OSRAM about different approaches on LED string diagnostic in automotive. Link here (PDF)

One requirement especially in automotive applications is the diagnosis of failures in functions and systems. Therefore light functions realized with LEDs like break light, daytime running light, low and high beam may require a diagnostics function. This application note describes some items which have to be taken into account, when a diagnostic function for a LED string or a multi LED module has to be realized.

App note: Challenge and Response with 1-Wire® SHA Devices

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Another app note from Maxim Integrated about challenge-response security on 1-wire devices. Link here (PDF)

Challenge-response can be a secure way of protecting access to any privileged material if implemented correctly. In this document, many options for challenge-response access control are discussed but the most secure method given is presenting a different random challenge on each access attempt and having a response that only the host can interpret without giving out any secrets. This document shows why Maxim’s SHA-1 iButtons® and 1-Wire devices are ideal choices when implementing this kind of challenge-response system

App note: Recommendations to avoid short pulse width issues in HVIC gate driver applications

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Application note from ON Semiconductors discussing possible abnormalities on High voltage gate driver when operating on short pulses. Link here (PDF)

The High−Voltage Integrated Circuit (HVIC) gate driver family is designed to drive an N−channel MOSFET or IGBT up to 600 V. One of the most common methods to supply power to the high−side gate drive circuitry of the high−voltage gate drive IC is the bootstrap power supply. This bootstrap power supply technique has the advantage of being simple and low cost. However, duty cycle is limited by the requirement to charge the bootstrap capacitor and serious problems occur when extremely short pulse width is used in the application system. This application note explains the features of HVIC gate drivers and provides recommendations to avoid short pulse−width issues in the application.

App note: High voltage inverting buck reduces complexity and board space

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App note from ON semiconductors about repurposing a buck converter to produce negative voltages. Link here (PDF)

Applications in the electronics industry ranging from sensor−based designs to power amplifiers are periodically faced with the requirement to generate a negative voltage rail. Although many transformer−based designs, charge pumps and other methods have been used to meet such a requirement, the inverting buck−boost topology stands out as simple to design and can save on power and board space too.

With power budgets in many applications already stretched, and PCB real estate limited due to the high levels of functionality incorporated in many new products, power devices that use an inverting buck−boost topology can prove extremely valuable to systems designers.

A Buck regulator can be reconfigured to generate a negative output voltage from a positive input voltage using the inverting buck−boost topology. Unlike a buck regulator, the Inverting buck−boost transfers energy to the output through the output diode during the ’Off’ time. For this reason, users must keep in mind that the average output current is always less than the average inductor current.

App note: The reduction of input voltage spike on power switches

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Another app note from Richtek introducing solutions for reducing the input voltage spike on power switches. Link here

The power switch is a low voltage, single N-Channel MOSFET high-side power switch, optimized for self-powered and bus- powered Universal Serial Bus (USB) applications.

In worse operating condition, an input voltage spike may over the chip’s maximum input voltage specification to damage the chip.

App note: Analyzing VIN overstress in power ICs

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Investigative app note from Richtek about the component failure point caused by EOS. Link here (PDF)

Failures in power ICs are often the result of Electrical Over Stress (EOS) on the IC input supply pin. This report explains the structure of power IC input ESD protection and how ESD cells can become damaged due to EOS. Common causes for input EOS are hot-plug events and other transient effects involving wire or trace inductance in combination with low ESR ceramic capacitors. Solutions are presented how to avoid EOS via special circuit and system design considerations.