The necessity to step down excessive bus voltages to decrease voltages to energy ICs and different masses is rising throughout quite a lot of programs together with automotive, industrial automation, telecommunications, computing, white items, and shopper electronics. The problem for designers is to execute this down-conversion with most effectivity, minimal thermal loading, at low price, and with the smallest attainable answer measurement.
Standard asynchronous buck converters supply a doubtlessly low-cost answer, but in addition have decrease conversion efficiencies that don’t meet the wants of many digital programs. Designers can flip to synchronous DC/DC converters and synchronous DC/DC controllers to develop compact options that ship excessive efficiencies.
This text briefly describes the efficiency necessities of digital programs for high-efficiency DC/DC conversion and opinions the distinction between asynchronous and synchronous DC/DC converters. It then introduces a number of synchronous DC/DC converter design choices from Diodes, Inc., STMicroelectronics, and ON Semiconductor together with analysis boards and design steering that may jump-start growth of high-efficiency options.
Why synchronous DC/DC converters are wanted
The rising necessities for greater effectivity in all forms of digital programs mixed with rising system complexities is leading to a corresponding evolution of energy system architectures and energy conversion topologies. With a rising variety of impartial voltage domains to assist rising performance, distributed energy architectures (DPAs) are being utilized in an increasing number of digital programs.
As an alternative of getting a number of remoted provides to drive the assorted masses, a DPA has one remoted AC/DC energy provide that produces a comparatively excessive distribution voltage, and a number of, smaller buck converters that down convert the distribution voltage to a decrease one as required by every particular person load (Determine 1). Using a number of buck converters affords some great benefits of smaller measurement, greater effectivity, and higher efficiency.
Determine 1: Distributed energy structure displaying the primary remoted AC/DC energy provide (entrance finish) and the a number of non-isolated DC/DC converters powering low voltage masses. (Picture supply: Digi-Key Electronics)
The method of choosing between asynchronous and synchronous buck converters relies on the tradeoffs between price and effectivity. If a lowest answer price is required and decrease effectivity and better thermal loading could be accepted, an asynchronous buck answer could also be most popular. However, if effectivity is the precedence and a cooler working answer is most popular, the next price synchronous buck converter is mostly the superior selection.
Synchronous vs. asynchronous buck converters
A typical asynchronous buck converter software is proven in Determine 2. The LM2595 from ON Semiconductor is a monolithic built-in circuit that features the primary energy change and the management circuitry. It’s internally compensated to reduce the variety of exterior elements and simplify the ability provide design. It delivers a typical conversion effectivity of 81% and dissipates 19% of the ability as warmth, whereas a synchronous buck answer can have a typical conversion effectivity of about 90%, dissipating solely 10% of the ability as warmth. That implies that the thermal losses in an asynchronous buck converter are almost twice as giant because the thermal losses in a synchronous buck converter. Subsequently, the usage of a synchronous buck converter significantly simplifies thermal administration challenges by decreasing the quantity of warmth generated.
Determine 2: Typical asynchronous buck converter software displaying the output rectifier (D1), the output filter (L1 and Cout), and the suggestions community (Cff, R1 and R2). (Picture supply: ON Semiconductor)
In a synchronous buck converter, such because the ST1PS01 from STMicroelectronics, the output rectifier is changed by synchronous MOSFET rectification (Determine 3). The decrease “on” resistance of the synchronous MOSFET in contrast with the output rectifier in an asynchronous buck converter reduces losses and leads to considerably greater conversion efficiencies. The synchronous MOSFET is inside to the IC, eliminating the necessity for an exterior rectifier diode.
Determine 3: Synchronous buck software circuit displaying the elimination of the exterior output rectifier diode. Output filtering and suggestions elements are nonetheless required. (Picture supply: STMicroelectronics)
There’s a price for the upper effectivity and decrease thermal loading made attainable with a synchronous buck converter. With a single energy switching MOSFET and a diode for rectification, asynchronous buck converter controllers are a lot easier (and smaller) since they don’t have to take care of the potential of cross-conduction or “shoot-through”, and there’s no synchronous FET to regulate. A synchronous buck topology requires a extra sophisticated driver and anti-cross conduction circuitry to regulate each switches (Determine 4). Making certain that each MOSFETs don’t activate on the identical time and create a direct brief requires extra complexity and leads to bigger and costlier ICs.
Determine 4: Synchronous buck converter IC block diagram displaying the 2 built-in MOSFETs (subsequent to the pin marked ‘SW’) and the added Driver/anti-cross conduction circuitry. (Picture supply: STMicroelectronics)
Though pulse width modulation managed synchronous buck converters are extra environment friendly below average or full load circumstances, asynchronous buck converters usually ship greater conversion efficiencies below gentle load circumstances. That, nonetheless, is changing into much less and fewer the case as the most recent synchronous buck converter implementations embody a number of working modes that allow designers to optimize low load efficiencies.
Synchronous buck for five volt and 12 volt energy distribution
For designers utilizing 5 and 12 volt energy distribution in shopper merchandise and white items, Diodes, Inc. affords the AP62600, a 6 ampere (A) synchronous buck converter with a large enter vary of 4.5 to 18 volts. The gadget integrates a 36 milliohm (mΩ) high-side energy MOSFET and a 14 mΩ low-side energy MOSFET to offer high-efficiency step-down DC/DC conversion.
The AP62600 wants minimal exterior elements on account of its fixed on-time (COT) management. It additionally delivers a quick transient response, simple loop stabilization, and low output voltage ripple. The AP62600 design is optimized for electromagnetic interference (EMI) discount. The gadget has a proprietary gate driver scheme to withstand switching node ringing with out sacrificing MOSFET turn-on and turn-off occasions, which reduces high-frequency radiated EMI noise attributable to MOSFET switching. The gadget is offered in a V-QFN2030-12 (Sort A) bundle.
There’s a power-good indicator which alerts customers to any fault circumstances that will come up. A programmable soft-startup mode controls inrush present at power-up, enabling designers to implement energy sequencing when utilizing a number of AP62600s to produce giant built-in units, corresponding to discipline programmable gate arrays (FPGAs), software particular ICs (ASICs), digital sign processors (DSPs), and microprocessor items (MPUs).
The AP62600 provides designers a selection of three operation modes to satisfy the precise wants of particular person purposes (Determine 5). Excessive effectivity could be realized throughout all masses with pulsed frequency modulation (PFM) operation. Different modes accessible embody pulse width modulation (PWM) to get one of the best ripple efficiency, and an ultrasonic mode (USM) which avoids audible noise at gentle masses.
To assist designers begin utilizing the AP62600, Diodes, Inc. affords the AP62600SJ-EVM analysis board (Determine 6). The AP62600SJ-EVM has a easy structure and permits entry to the suitable alerts by way of check factors.
Synchronous buck for 24 volt buses
The L6983CQTR from STMicroelectronics incorporates a 3.5 to 38 volt enter vary and delivers as much as Three A of output present. Designers can use the L6983 in a variety of purposes, together with 24 volt industrial energy programs, 24 volt battery-powered gear, decentralized clever nodes, sensors, and always-on and low-noise purposes.
The L6983 relies on a peak present mode structure with inside compensation and is packaged in a Three mm x 3mm QFN16, thereby minimizing design complexity and measurement. The L6983 is offered each in low consumption mode (LCM) and low noise mode (LNM) variations. LCM maximizes the effectivity at gentle masses with managed output voltage ripple, making the gadget appropriate for battery-powered purposes. LNM makes the switching frequency fixed and minimizes the output voltage ripple for gentle load operations, assembly the specification for noise delicate purposes. The L6983 permits the switching frequency to be chosen within the 200 kilohertz (kHz) to 2.Three megahertz (MHz) vary with non-obligatory unfold spectrum for improved EMC.
STMicroelectronics affords the STEVAL-ISA209V1 analysis board to allow designers to discover the capabilities of the L6983 synchronous monolithic step-down regulator and jump-start their designs.
Synchronous buck controller for computing and telecom designs
The NCP1034DR2G from ON Semiconductor is a excessive voltage PWM controller designed for top efficiency synchronous buck DC/DC purposes with enter voltages as much as 100 volts. This gadget is designed to be used in 48 volt non-isolated energy conversion in embedded telecommunications, networking and computing purposes. The NCP1034 drives a pair of exterior N−channel MOSFETs as proven in Determine 7.
The NCP1036 incorporates a programmable switching frequency from 25 kHz to 500 kHz and a synchronization pin that enables the switching frequency to be externally managed. Offering each these frequency controls permits designers to pick the optimum worth for every particular software and to synchronize the operation of a number of NCP1034 controllers. The gadget additionally contains consumer programmable undervoltage lockout and hiccup present restrict safety. For low voltage designs, an internally trimmed 1.25 volt reference voltage can be utilized for extra exact output voltage regulation.
4 undervoltage lock-out circuits are included to guard each the gadget and the system. Three are devoted to particular features; two defend the exterior high-side and low-side drivers, and one protects the IC from beginning prematurely earlier than VCC is below a set threshold. The fourth undervoltage lock-out circuit could be programmed by the designer utilizing an exterior resistor divider: so long as VCC is beneath the consumer set threshold worth, the controller stays off.
To assist designers get began utilizing the NCP1034, ON Semiconductor affords the NCP1034BCK5VGEVB analysis board (Determine 8). This eval board was designed with a number of choices to assist quite a lot of system wants. There’s a linear regulator powering the IC, and the designer can select whether or not it does so utilizing both a Zener diode or a excessive voltage transistor by deciding on the suitable resistor. Designers even have a selection of second sort (voltage-mode) compensation or third sort (current-mode) compensation, selectable ceramic or electrolytic output capacitors, and numerous enter capacitance values. There are two header pins: one for simple connection to an exterior synchronization pulse supply to permit the board to attach on to the opposite NCP1034 demo board; the opposite to connect with the SS/SD pin that can be utilized to close down the controller by connecting it to floor.
The necessity to step down excessive bus voltages to decrease voltages to energy ICs and different masses is more and more required throughout quite a lot of programs together with automotive, industrial automation, telecommunications, computing, white items, and shopper electronics.
As proven, designers can flip to synchronous buck energy converters to implement this down-conversion with most effectivity, minimal thermal loading, at low price, and with the smallest attainable answer measurement.