1. Regarding the issue of buck regulator systems with wide or high input range and low power output: Generally, switching regulators are often used to reduce unstable wide and high input voltages to stable low output voltages. For systems that must reduce input voltage through DC/DC conversion, switching regulators can significantly improve conversion efficiency, far superior to linear regulators in this respect. Their pulse width modulation (PWM) power supply controllers have single-ended and dual-ended topologies. 1.1 Control methods and characteristics of single-ended topologies: There are two control methods: voltage mode and current mode. Voltage mode is a simple, low-noise control method that can meet the needs of large input and output ranges. Current mode has built-in current limiting and fast transient response time. Integration: Integrated soft-start (programmable) provides predictable startup capability, while built-in leading-edge blanking circuitry is used to suppress glitches caused by MOSFET turn-on transitions. Performance features include: multiple voltage-mode controllers with input voltage feedforward capability, enabling immediate response to changes in input line voltage; most controllers have built-in high-current drive capability; no external MOSFET driver required; lower startup current for offline applications; low operating current for high efficiency under low loads; programmable minimized duty cycle limits for high efficiency under low loads (e.g., UCC3581). Characteristics: Offline operation from 10W to 350W, DC/DC power supply; single-ended topology power supply (buck, boost, flyback, and forward). 1.2 Dual-ended topology control methods and characteristics: Its current-mode control technology employs cycle-by-cycle current limiting and is characterized by its fast transient response; while voltage-mode is a versatile, low-noise control method capable of achieving a large duty cycle range. Soft-switching features: Zero-voltage switching (ZVT) soft-switching technology minimizes power loss during startup; phase switching and zero-voltage switching controllers maximize the efficiency of the full-bridge converter. Protection Features: Flexible overcurrent limiting loop provides programmable error protection modes; programmable soft-start enables predictable startup during initialization and after errors; high-speed, cycle-by-cycle current limiting; maximized duty cycle limit to prevent transformer saturation; programmable deadtime control to prevent cross-conduction of power switches. 1.3 Example Application—Higher Integration PWM Controller MAX5051 The MAX5051 is a dual-switch topology PWM controller, ideal for establishing high-performance, synchronous rectified, 48V isolated power supplies. See Figure 1 for a schematic diagram of MAX5051 function pins and applications. Its component count is reduced by 2 times while cost is reduced by 3 times. [img=450,361]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379001.gif[/img] It should be said that most DC/DC converters with built-in transformers today use flyback and forward circuitry. Since the transformer turns ratios of these two layouts can be set according to different requirements, most buck conversion requirements can be met, ensuring that applications with wide and high input/output buck ratios can also fully utilize conversion performance. For systems that do not require grounding insulation, buck regulators are a more ideal circuit layout. The advantage of buck regulator circuit layouts is lower cost, as this solution does not require a transformer. The following is the voltage conversion formula for buck regulators: Vout = VIN × D. 2. Design and Application of New Integrated Switch DC/DC Converters 2.1 Design Concept Efficiency and Small Size Solution. If the highest conversion efficiency and the smallest solution size are required simultaneously, then using an inductive converter with an integrated switch is an ideal choice. Low-power DC/DC converter series and point-of-load step-down DC/DC converters can achieve peak efficiencies of 97%, such as T1's TPS6xxxx and TPS54xxx. Its synchronous correction not only replaces the expensive Schottky correction diodes, but also improves converter efficiency by up to 10%. Higher efficiency means additional operating time for battery-powered applications, while lower power consumption in high-current applications relaxes the requirements for thermal design. Since only resistors, capacitors, and a single inductor are needed externally for operation, integrated high-side and low-side switching FETs effectively reduce board space. Depending on the output current, the integrated switching DC/DC converter can be packaged in the following ways: CSP (800mA), SOT-23 (400mA), QFN-10 (1.2A), and TSSOP-28 (13A), further reducing the solution size. Regarding output current—the output current is typically limited by the size of the integrated FETs and is rated for the minimum input voltage, such as the TPS6xxxx series. The TPS54xxx series, however, indicates a continuously available output current; higher peak currents can be achieved to ensure adequate power supply during startup of high-performance DSP, FPGA, and ASIC systems. A rough estimate of the output current can be achieved using the following equation: Lout = 0.65 × Iswitch(min) × (Vin × Vout). For applications with output current below 300mA and efficiency below 90%, inductorless charge pump DC/DC regulators offer a cost- and space-efficient option. Regarding input voltage, DC/DC converters can operate with a wide range of input sources, including power modules, wall supplies, and batteries. The TPS6xxxx series and their small form factor packages, along with low quiescent current, are optimized for low-power battery-driven applications. For battery-driven systems, the input voltage varies significantly with battery discharge. Therefore, the choice of converter must depend on the given battery technology level and quantity. For example, the TPS54xxx SW1FT series can operate with pre-regulated bus voltages of 24V, 12V, 5V, or 3.3V. Regarding output voltage, current advanced DSPs, FPGAs, and ASICs require lower supply voltages. For maximum flexibility, converters can support both rated and adjustable output voltages down to 0.7V. 2.2 Application Example – 5.5V to 36V Input, 3A Step-Down DC/DC Converter TPS5430 The TPS5430 3A DC/DC converter is ideal for a wide range of applications using common 12V or 24V power rails. The appropriate SWIFT software tools significantly reduce development time. Figure 2 shows the TPS5430's functions and applications. Its main features include: integrated 110mΩ N-channel MOSFET; fixed 500kHz switching frequency; adjustable output voltage down to 1.23V; built-in compensation, built-in slow start, and built-in bootstrap diode; voltage feedforward, built-in overcurrent protection, and thermal shutdown; only 18μA shutdown quiescent current; operating junction temperature range of -40℃ to 125℃; package: miniaturized thermally enhanced 8-pin S01CPower PAD package. [img=408,248]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379002.gif[/img] Application Areas: In consumer applications, such as set-top boxes, DVDs, and LCD displays; it can also be used in industrial and automotive audio power supplies and battery chargers, high-power LED power supplies, and 12/24-V distributed power systems. 3. Typical Application Examples of High and Wide Input Range DC/DC Buck Regulator Systems Figure 3(a) MAX5090 Function and Application Schematic Diagram: It can integrate a 76V input, low quiescent current, 2A buck DC-DC converter. Its features include: no need for MOV or TVS; wide input voltage range of 6.5V to 76V; withstands automotive load shedding up to 80V; high performance with 92% efficiency at full load, low quiescent current of 310μA and low shutdown current of 19μA at no load; designed for harsh automotive environments, ensuring operation over a junction temperature range of -40°C to +125°C, hiccup-mode short-circuit protection to keep the device cool, thermal shutdown, and short-circuit current limiting. All these features can be integrated into a 5mm x 5mm TQFN package. 3.2 The MAX5089, a 2A DC-DC converter with the highest frequency and wide input voltage range (5V to 23V), is shown in Figure 3(b). Its features include: a 2.2MHz switching frequency, avoiding noise-sensitive AM or ADSL2+ bands; a wide Vin range of 5V±10% or 5.5V to 23V, suitable for a wide range of automotive voltages and ideal for regulating wall adapters with a wide voltage range for xDSL and set-top boxes, as well as for controlling coarse-tuned intermediate bus voltages from 7V to 14V; and high efficiency, with a synchronous rectifier driver allowing for maximum efficiency over the wide Vin range. Figure 3(b) shows a schematic diagram of the MAX5089's functions and applications. [img=417,276]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379003.gif[/img][img=428,214]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379004.gif[/img] 4. Application of Simulated Current Sensing Signal Technology in DC/DC Buck Regulator Design 4.1 Introduction of Simulated Current Sensing Signal Technology Common modulation control methods for buck regulators include voltage mode (VM), current mode (CM), and constant on-time (COT). Current mode control can easily provide loop compensation and also has line feedforward compensation, making it popular among power supply system designers. Generally speaking, voltage mode control is not easily affected by noise, but its transient response and stability are not as good as current mode. If a constant on-time control method is used, most stability problems will automatically disappear, and the transient response of the line and load will be relatively ideal. However, a regulator using constant on-time control does not operate at a constant switching frequency, and therefore cannot be synchronized with an external clock. Traditional current-mode control methods have their drawbacks. Figure 4 shows a block diagram of a buck regulator using current-mode control. The regulator's output voltage is not only monitored but also compared with a reference voltage. Once an error signal occurs, it is transmitted to the pulse width modulator (PWM). Voltage-mode and current-mode control methods are completely different because their modulation ramp signals come from different signal sources. The modulation ramp signal required to perform the current-mode control function is a signal proportional to the buck switch current. The inductor current flows into the buck switch during the switch's conduction period. After energization, the slope of the inductor current waveform is a positive number (VIN - Vout)/L. The measured value of the buck switch current must be accurate, and the relevant data must be measured as soon as possible to generate the modulation ramp signal. The main drawback of current-mode control is the difficulty in obtaining the buck switch current signal. [img=500,322]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379005.gif[/img] 4.2 Characteristics of Simulated Current Sensing Signal Technology It is not easy to quickly and accurately measure the current of a buck switch, but a new method can be used to simulate the buck switch current without actually measuring the current, thus avoiding the accuracy problem. Taking a buck regulator as an example, the inductor current is the sum of the buck switch current and the freewheeling (freewheeling) diode current (Figure 5 shows a schematic diagram of the buck regulator waveform using simulated current sensing signal technology). The buck switch current waveform consists of two parts: a basic or blanking level signal and a ramp signal. The blanking level signal is the lowest inductor current value (valley) throughout the entire switching cycle. When the buck switch starts and the freewheeling (freewheeling) diode turns off, the inductor current is at its lowest value. When the inductor current is at its lowest point, the currents of the buck switch and diode are also at their lowest values. We can sample the current of the freewheeling diode using a sampling and holding method before the buck switch starts, and the obtained measurement value can be used to capture the blanking level signal. [img=448,338]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379006.gif[/img] Another component of the buck switch current waveform is the ramp signal. The inductor voltage is the input/output voltage difference after the buck switch starts. This voltage is strong enough to input a ramp current with a positive slope into the inductor and buck switch. The slope of the ramp current is di/dt = (VIN - Vout)/L. An appropriate ramp capacitor value CRAMP can be selected to ensure that the capacitor voltage slope is proportional to the inductor current slope. 4.3 Examples of Applications of Simulated Current Sensing Signal Technology 4.3.1 Figure 6 is a block diagram of the LM25576 chip. This chip is one of the six newly launched highly integrated buck regulators, characterized by the aforementioned simulated current mode control design. The top of the figure shows the power switch typically used in buck regulators. The controller connects the anode of the freewheeling diode to ground, while the low-current sensing resistor and amplifier are responsible for measuring the diode current. The sampling and holding circuit triggers the start of each cycle before the buck switch is activated. A blanking level signal is provided for the simulated current sensing signal. [img=442,269]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379007.gif[/img] The LM25576 chip can detect input and output voltages to generate drive current. It charges the external ramp capacitor CRAMP. During each cycle after the buck switch starts, the capacitor voltage rises linearly. After the buck switch closes, the ramp capacitor discharges. To ensure proper operation, the ramp capacitor value must be proportional to the output inductor's inductance. Initially, the following ramp capacitor values ​​are recommended: (Note: L in the formula is in Heny, while CRAMP is in Farad.) The final necessary step in generating the analog buck switch current signal is to add the blanking level signal from the sampling and holding circuit to the ramp capacitor voltage signal. This allows the controller to perform similar peak current mode control, but without delay or transient response in the current sensing signal. For applications with a duty cycle exceeding 50%, peak current mode control regulators may exhibit subharmonic oscillations. Adding a fixed-slope voltage ramp signal above the current sensing signal can prevent this oscillation. For example, in a ramp generator circuit, an additional 25 μA fixed bias current provides an extra fixed ramp for the capacitor voltage ramp signal. For applications with extremely high duty cycles, pull-up resistors can be used to compensate for the insufficient 25 μA bias current. The capacitance of the ramp capacitor can also be reduced to increase the slope and prevent subharmonic oscillations in the regulator. 4.32 Current-mode, ultra-high accuracy PWM synchronous buck controller: Using the LM3495 controller offers the following advantages: the highly sensitive submicron processor not only provides greater design flexibility but also allows for the addition of reliable protection functions. Figure 7 shows the block function and application diagram of the LM3495 chip. [img=99,27]http://cms.cn50hz.com/files/RemoteFiles/20090204/139379008.gif[/img] Product features: 2.9V to 18V input voltage; 0.6V to 5.5V adjustable output voltage; feedback voltage accuracy of ±1% (within the specified temperature range); current-mode control to withstand large input-to-output voltage drops; operation with only one input power supply; pre-biased start-up to output; hiccup-mode current limiting protection to ensure less heat dissipation; internal soft-start with tracking capability; switching frequency from 200kHz to 1.5MHz, adjustable to synchronize with the system for controlling system noise; TSSOP-16 package. Applications: Suitable for power supply systems of application-specific integrated circuits (ASICs), FPGAs, digital signal processors, embedded controllers, industrial systems, and high-output-current power management modules. [tr][/tr][td] [/td]