Start with several practical circuits, and interpret several application scenarios to achieve low electromagnetic interference in complex electronic systems

For the majority of system manufacturers such as automobiles, communications, and test and measurement equipment, technological development has brought about significant improvements in terminal functions and performance. The root cause is the more abundant Electronic modules equipped in the system. However, the richer the functions, the more complex the circuit, whether it is a centrally-controlled integrated multimedia system, a high-performance audio system, or a smaller and smaller 5G communication device (mobile phone and base station) in a new car, or more and more requirements The higher the instrumentation, the more stringent the requirements for high digital and analog ICs, especially in terms of power supply requirements.

For the majority of system manufacturers such as automobiles, communications, and test and measurement equipment, technological development has brought about significant improvements in terminal functions and performance. The root cause is the more abundant electronic modules equipped in the system. However, the richer the functions, the more complex the circuit, whether it is a centrally-controlled integrated multimedia system, a high-performance audio system, or a smaller and smaller 5G communication device (mobile phone and base station) in a new car, or more and more requirements The higher the instrumentation, the more stringent the requirements for high digital and analog ICs, especially in terms of power supply requirements.

As an indispensable part of any electronic system design, the level of power supply performance has a vital impact on the level of system performance. The electromagnetic interference (EMI) characteristic is one of the key performances. This interference affects the circuit through electromagnetic induction, electrostatic coupling, or conduction. Any requirements for power supply performance (increased power density, higher switching frequency, and greater current) will amplify the impact of EMI. Therefore, if it is not considered in the initial design stage, it will seriously affect the product’s performance and time to market. In response to this situation, ADI has introduced a Silent Switcher series architecture regulator solution designed for low EMI scenarios.

Silent Switcher architecture eliminates EMI interference like this

The commonly used EMI control standard is CISPR 25 Class 5, which specifies acceptable limits for frequencies from 150 kHz to 1 GHz. To meet this requirement, it usually involves complex design and test procedures, including trade-offs in many aspects such as solution size, overall efficiency, reliability, and complexity. Traditional methods control EMI by slowing down the switching edge or reducing the switching frequency. The disadvantages of this are reduced efficiency, increased switching time, and increased solution size. Alternative mitigation solutions include large and complex EMI filters, buffers, or metal shields, which can significantly increase the cost of board space, components, and assembly, and complicate thermal management and testing.

The Silent Switcher step-down regulator is designed to provide high efficiency and ultra-low electromagnetic interference radiation at high switching frequencies (>2 MHz), thereby realizing a very compact and low-noise step-down solution. This series adopts special design and packaging technology: in design, the thermal circuit is divided into two circuits with opposite polarities to form a local magnetic field that can cancel each other; on the package, the silicon chip is flipped and copper pillars are added. Shorten the distance from the internal FET to the package pin and input capacitance to reduce the range of the thermal loop. Using the above technology, Silent Switcher can achieve >92% efficiency at 2 MHz, while easily complying with CISPR 25 Category 5 peak EMI limits.

Start with several practical circuits, and interpret several application scenarios to achieve low electromagnetic interference in complex electronic systems

Magnetic field cancellation in Silent Switcher regulator

The internal structure of the new generation Silent Switcher 2 technology uses copper pillars instead of bonding wires, adds internal bypass capacitors, and an integrated substrate ground plane to further improve EMI, making it insensitive to PCB layout, which can simplify design and Reduce performance risk.

Typical Silent Switcher application schematic diagram and its appearance on the PCB

Several typical application scenarios using Silent Switcher architecture

1

Respond to automotive high-current applications

Automotive applications require that the system does not generate electromagnetic noise that may interfere with the normal operation of other automotive systems. For example, a switching power supply is a high-efficiency power converter, but it generates undesirable high-frequency signals that may affect other systems. Switching regulator noise occurs at the switching frequency and its harmonics. Sensors and other instruments affected by this type of noise may operate abnormally, causing audible noise or serious system failure.

The figure below shows a low IQ (quiescent current), low noise solution that supports high current applications for automotive I/O and peripherals. The front-end LT8672 protects the circuit from battery reverse faults and high-frequency AC ripple, and the forward voltage drop is only tens of mV. The LT8650S has a switching frequency of 400 kHz, an input range of 3 V to 40 V, and an output capacity of 8 A when the two channels are operated in parallel. Two decoupling capacitors are placed close to the input pins of the LT8650S. Due to the Silent Switcher 2 technology, the high-frequency EMI performance is excellent even without the EMI filter installed. The system complies with CISPR 25 Class 5 peak and average limit requirements, and has a large margin.

LT8672 and LT8650S are configured for high output power

The figure below shows the average test result of the vertically polarized radiated EMI in the range of 30 MHz to 1 GHz. The complete solution has the characteristics of simple schematic diagram, very few total components, compact size, etc., and the EMI performance is not affected by changes in the circuit board layout.

LT8672 and LT8650S EMI performance: 30 MHz to 1 GHz

2

Cope with wide dimming ratio LED lighting applications

Many applications of LED lighting require a wide dimming ratio. Take cars as an example. The LED backlights used in car head-up displays, infotainment systems, and instrument panel lighting must have sufficient brightness to compete with the direct sunlight that continuously floods into the car during the day, and it can also reduce the brightness by a few degrees. An order of magnitude to avoid instantaneous blindness of the driver at night. Such extreme LED dimming requirements will be difficult to meet the CISPR EMI standard without adding expensive noise reduction components and complexity.

The LT3932 incorporates many built-in functions aimed at minimizing EMI, making it possible to achieve both high dimming ratio and low EMI at the same time:

With its Silent Switcher® architecture for low EMI thermal loops, EMI is minimized.

The built-in spread spectrum frequency modulation (SSFM) function circuit helps reduce conducted and radiated EMI.

The conversion rate of the LT3932 is controlled to optimize efficiency while maintaining low noise performance.

The 2MHz automotive LED driver has low EMI and internally generated PWM dimming and 90% peak efficiency over the entire input range (~91% efficiency without EMI filter)

The LT3932 synchronous step-down LED driver integrated with a 36V, 2A switch integrates its high-efficiency integrated power switch in a small form factor 4mm x 5mm QFN package, and can operate at a switching frequency of up to 2MHz, suitable for compact and high-bandwidth designs . With built-in fault protection to handle open and short LEDs, and spread spectrum frequency modulation designed to help reduce EMI, the LT3932 can meet the demanding requirements of automotive and industrial LED lighting applications.

LT3932 circuit passed CISPR 25 Class 5 radiated average EMI test

3

Respond to high test and measurement applications

In order to ensure high performance, precision test and measurement systems require power solutions with low ripple and radiated noise, so as not to degrade the performance of the high-resolution converter signal chain. In these test and measurement applications, generating bipolar and/or isolated system power supplies presents system designers with board area, switching ripple, EMI, and efficiency challenges.

Many precision test and measurement instruments (such as source meters or power supplies) require multi-quadrant operation to acquire and measure positive and negative signals. This requires efficient generation of positive and negative power from a single positive power input with low noise. Use Silent Switcher, μModule regulator LTM8074 to improve the high efficiency solution to lower voltage as shown in the figure below.

A power supply solution that reduces the voltage to a lower voltage rail under the condition of low EMI

LTM8074 is a Silent Switcher, ?Module step-down regulator in a small 4 mm × 4 mm BGA package that can provide up to 1.2 A current with low radiation noise. This module device has high efficiency and extremely low radiated noise, so it is the choice for powering noise-sensitive precision signal chains. Depending on the PSRR connected to power-powered components such as amplifiers, DACs, or ADCs, it may be possible to power them directly from the output of the Silent Switcher, without the need for an LDO regulator to further filter the power ripple, which is required for traditional switches. The high output current of 1.2A also means that it can be used to power digital hardware in systems such as FPGAs when needed. The small size and high integration of the LTM8074 make it ideal for space-constrained applications, while simplifying and accelerating the design and layout of the switching regulator power supply.

Summarize

Electronic systems are constantly developing and popularizing in the present and in the future. It is foreseeable that the requirements for low EMI are destined to become more and more stringent. Based on this, ADI will continue to develop the Silent Switcher architecture and continue to provide more and more solutions to help system designers more calmly deal with current and future challenges.

The Links:   G057QN01-V1 LM190E08-TLG1

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