Many options for establishing a high buck ratio

Designing a high buck-to-DC power converter is not an easy task, especially when converting 48 VDC inputs to the 3.3 VDC output and below, because maintaining high efficiency and low cost is extremely challenging. Such DC-to-AC converters are primarily needed in telecommunications systems and data center computers, which have modern DSPs, FPGAs, and Asics that require voltages from 3.3 V to lower. To avoid the construction of Gao Jie, the designer uses an intermediate bus converter to further reduce the popular 48 volt DC bus voltage in this system to 24 volts, 12 volts, or lower intermediate voltage levels. To simplify the design of a distributed power architecture, this adds a step. This increases the cost and space of the system board, while reducing overall efficiency performance.

Over the years, in order to eliminate the intermediate power conversion phase, some manufacturers have produced high-efficiency, high-density buck gearbox, at the expense of higher costs. For example, Vicor has combined its silicon-based building blocks, such as the PRM and VTM modules, to generate a standalone DC-to-DC solution that requires 48 VDC bus voltages and translates them into a low processor core voltage of 1 V, To comply with Intel's VR12.0 and VR12.5 specifications. Recently, Vicor expanded its Picor Cool power series of high-density, isolated DC-to 0-voltage conversion (ZVS) converter modules, with new members providing a V input and 3.3 v output of A. One example is Pi3101-00hviz.

At the same time, efficient power conversion (EPC) demonstrates a non-isolated buck converter from V to 1.2 v through its enhanced mode Gan (EGaN) FETs2. The initial demonstration of the EPC included the first generation of 100-D Egan FETs, such as EPC1001 and EPC1007, enabling the non-isolated buck converter to run from the 48v input and produce a low output of 1.2 v. According to the supplier, next-generation products such as EPC2001 and EPC2007 can further improve efficiency in terms of higher reliability and cost competitiveness.

　　cost-Effective solutions

In the commercial power supply, the cost is equally important, so other suppliers such as Intersil, linear technology and Texas Instruments have adopted silicon wire to deliver high-buck ratio DC-to converter solutions in a high performance and low cost manner. More and more competitors are entering this field.

In Intersil, for example, it has recovered a high voltage synchronous Buck PWM Buck Controller ISL8117, which makes it possible to convert from a 48v input to a higher buck ratio conversion. According to Intersil, the low load cycle of the synchronous Buck PWM Controller (minimum of up to NS) enables direct buck conversion from a high voltage 48v input to a low load (POL) voltage of 1.2 V or lower. As a result, the supplier says, designers can reduce the complexity of the system and the cost of the solution while maintaining the performance of industrial, factory automation, medical and communications infrastructure applications.

Based on the ISL8117 data sheet, the PWM controller uses valley-current mode modulation with adaptive slope compensation to enable wide range of VIN and vout combinations to operate reliably without external compensation. In addition, system designers can use the controller's adjustable frequency of up to 2 MHz to optimize power supply costs, size and efficiency. The ISL8117 offers programmable soft-start and start-up functions, as well as a power led for easy track sequencing and other housekeeping needs. At the same time, according to the product data sheet, only about 10 external components are required to complete the high step-down-ratio Buck-converter solution with overvoltage/overcurrent/temperature protection, as shown in Figure 1. The PWM controller comes from a space-conscious 16-lead QFN and Htssop package. Both packages use Epad to improve heat dissipation and noise resistance.

Intersil ISL8117 Chart

Figure 1:isl8117 A control circuit driver with integrated MOSFET and protection circuitry simplifies the design of a high buck ratio conversion switch. It requires very few external components to complete the solution.

The efficiency of this converter depends on key parameters such as power MOSFET, switching frequency, inductor and other key parameters. If all other parameters remain constant, efficiency decreases as the vin/vout ratio increases. For example, if the peak efficiency is approximately 85% for a-V to 3.3 V/DC converter, and when the output is approximately 1 V, it will drop a few points and be entered at-V.

To assess the application of this controller in the real world, Intersil has designed two evaluation boards. The Low power evaluation Board ISL8117EVAL1Z is designed for high-current applications. Its electrical parameters include a 4.5-60 v input range, a switching frequency of up to khz, and an output current of 3.3 V output voltage of 6 A. The Overcurrent protection setting for this design is 8 A (minimum) at room temperature. Figure 2 shows a typical schematic for evaluating the controller. The measurement efficiency performance of this design is described in Figure 3 for different input voltages and fixed 3.3 v outputs.

Intersil isl8117eval1z schematic (click Full size)

Figure 2: Typical evaluation board schematic, 4.5-60 v input, 3.3 V output is 6 a.

Efficiency and output current diagram.

Figure 3: Efficiency and output current of the continuous current type (CCM) Gao Jie reduction inverter. The output is 3.3 v.

The peak efficiency of the input is observed to be approximately 78%, and the peak efficiency increases by more than 10 points when the input value drops to If the output of the same input is higher, the efficiency will rise, as demonstrated by the second High Power evaluation board ISL8117EVAL2Z, which is designed for the 18-60 v input and the five a V output. This high-power board is designed to deliver over 200w. A detailed BOM is provided in the user Guide, including output power MOSFETs and inductors, as well as measurement performance. Figure 4 shows the efficiency curve of the isl8117eval2z of the output plate of the V.

Efficiency and load current graph.

Figure 4: Efficiency of the continuous current-mode buck converter vs. the load current is 18-60 v input range, and the output is a.

As can be seen from Figure 4, when the input voltage is 48v, the peak efficiency is approximately 95%, significantly higher than the 3.3 V output converter. At the output of a V, the output ratio is only 4:1, while the 3.3 V output is 14.5:1. Internally, using ISL8117, the company has demonstrated a 48v input to 1v output converter at 10a and 200khz switching frequencies. The switching frequency is reduced and the overall efficiency of the design is improved. Internal tests have shown that the high buck ratio Buck Converter achieves a peak efficiency of 78% at full load and 80% peak efficiency at medium load when the external 5v bias is used.

　　More Options

Linear technology is another supplier interested in solving these problems. The company has released a 60 volt synchronous Buck Controller LTC3891, which enables efficient non-isolated high buck ratio conversion switches. The rated input range is 4 kv to 60 volts and the output voltage can be from 0.8 V to + V. The minimum duration for this section is up to NS and the switching frequency range is 50-900 kHz. The package option is 20-lead QFN or Htssop. The data sheet in this section gives a design example that handles an input voltage range of 4 V to 5 V with a low output power of 3.3 V for high efficiency. Figure 5 shows the typical efficiency of the 3.3 V output design and the relationship of the input voltage. It shows that as the input voltage increases, the efficiency decreases quickly.

The linear technique LTC3891 the efficiency of the input voltage curve and the graph.

Figure 5:ltc3891 Typical efficiency and input voltage curve of a high buck ratio converter. It shows that as the input voltage increases, the efficiency decreases quickly.

Similarly, TI has released TPS40170 to achieve a high buck ratio converter solution. The TPS40170 is a wide input synchronous PWM Buck controller with a width of 50 ns and a programmable frequency range of 600khz, voltage-controlled, input-voltage feedforward compensation. It is a 20-pin VQFN bag.

To sum up, as more and more suppliers see opportunities in this area, designers are increasingly choosing to build Gao Jie-drop buck converters. While some people prefer to offer a complete solution, from a 48v bus voltage to a low processor voltage, others decide to provide a high-voltage synchronous buck Controller. At the same time, EGaN FETs also entered the space to compete with the silicon wafer.