The relationship between analog power and digital power has been a hot topic in the industry. Which of the two technologies is more promising? Will the future show a “one-sided†trend? It happened that the two industry leaders came to visit and listened to what they said.
When dealing with load and efficiency, you have to look at the digital power supply.
Tom Spohrer, Product Marketing Manager, Microchip's 16-bit Microcontroller Division
Tom Spohrer, product marketing manager for Microchip's 16-bit microcontroller division, said digital power technology is better at dealing with load and efficiency. As shown in the Figure 1 CSCI efficiency requirements figure, to achieve the highest level of titanium standards, the device must achieve 96% efficiency at 50% load level. More difficult is that when the load level is 10%, the efficiency reaches 90%. At this point, traditional analog power technology is very difficult to implement, and many users turn to digital power.
He cited some of the more efficient practices currently used by customers, such as adaptive algorithms, including tangential, deadband adjustment, variable switching frequency, variable high voltage, and more. But he believes that doing so actually requires more computing resources. When dealing with transient response, the analog power supply is faster, but sometimes the efficiency is not high enough, and the advantage of the digital power supply is that when the load changes greatly and the expected output power is not reached, the real-time coefficient adjustment can be performed to adapt to the new load situation. . In addition, if a prediction algorithm is used, the digital power supply does not need to use the control loop damping control for pulse width modulation, and a reasonable value can be found between the maximum value and the minimum value, so that the power output reaches a certain target.
Industrial switching power supply integration trend
Lokesh Duraiappah, Intersil's director of industrial power market and applications, believes that the most important digital controller is the PMBus telemetry function, which can monitor the temperature, over-voltage and over-voltage functions of each load, so it is mainly used for power sequencing and voltage. Where there is a high demand for the balance. For example, applications such as computing, communications, and servers all use FPGAs. They have multiple voltage rails, and the power order is very important. At this time, the digital controller is more flexible than the analog controller. However, for industrial applications, they often do not require particularly high power, and the circuit is not particularly complicated. There is no strict requirement for the PMBus telemetry function, but the demand for board space, efficiency, and load point problems is strong. Therefore, the analog controller is more suitable.
But he also pointed out that the market is now increasingly eliminating the need to convert high-voltage (such as 40V, 36V, 42V) into low voltage (including 3.3V, 5V or 1V). In addition, with the increasing complexity of FPGAs, MCUs, and ASICs, the increase in the number of voltage rails, and the increase in the use of backup batteries, they are becoming a new trend in the development of industrial general-purpose power supplies.
Figure 2 shows the integration trend of industrial switching power supplies: the green area represents the technology of the existing fully integrated synchronous buck regulator, that is, all the modulators, drivers, and power MOSFETs are integrated in one IC; the blue area represents A discrete product solution for power MOSFETs and modulators. Lokesh Duraiappah said that a decade ago, the green area was much smaller than the blue area, but with the development of LDMOS technology, more and more integrated solutions were developed. However, in the case of high input voltage and low current, only the controller + external power MOSFET solution can be selected.
Digital power, no best, only better
Microchip has announced the introduction of the dsPIC33EP "GS" family of digital signal controllers (DSCs) with 14 new devices that enable more complex nonlinear prediction and adaptive control algorithms at higher switching frequencies. Designed to achieve better energy efficiency and power specifications. In addition, higher switching frequencies allow designers to develop higher density, smaller power supplies at a lower cost. Compared to the previous generation of DSC products, the new dsPIC33EP "GS" device can reduce latency by half the time when applied to a three-pole three-zero compensator, and can save up to 80% in any application.
In fact, the performance of this new product can be improved, there are three most important reasons: First, the new core with a frequency of 70MIPS to replace the previous 50MIPS core; Second, the integration of new registers in the new kernel; Third, double the ADC speed.
"This field-selected register set is almost instantaneous for field switching." Tom Spohrer said that the new series integrates three working registers, one for normal operation and two for standby. Each register set is assigned a specific interrupt priority level. When another interrupt service routine is called from one interrupt service routine (ISR), the data is saved, which reduces the saving and recovery of the register contents, which increases the compensator speed by about 50%. Shortened the delay of the control loop.
Five 12-bit ADCs provide 16Msps of total throughput and 300 nanoseconds of ADC latency, with early interrupts minimizing ISR overhead. Up to 22 analog ADC inputs, each with a dedicated result register and a differential input; the autonomous digital comparator compares the result to the threshold voltage and generates an interrupt in the event of overvoltage, undervoltage, and out of range conditions. It does not occupy CPU resources and has higher performance. In the process from ADC to PWM update, the new device reduces the delay time by a factor of about two.
The GS Series devices also integrate a variety of other advanced features such as instant update flash for applications that are particularly useful for high availability or "always on" systems; four analog comparators are equipped with 12-bit DACs for more demanding designs Two on-chip programmable gain amplifiers for current sensing and other precision measurements. Tom Spohrer specifically mentions the ability to change the working power firmware (such as active compensation calculation code, etc.) while maintaining continuous adjustments for instant updates. This function is implemented by dual flash partitioning. The existing code runs in the first flash partition, and the updated part of the code runs in the second flash partition. The conversion between the two can be completed within 300 nanoseconds, so that the entire power supply process is Implement code changes without any impact.
How many parameters do I choose for industrial power?
In high input voltage applications where lower output voltages are required, engineers typically rely on modules that increase system cost, or secondary DC/DC solutions that increase solution size and complexity. However, Intersil's first IVV-free synchronous step-down controller, the ISL8117, has been introduced by Intersil to provide an economical and reliable alternative to low output voltage/input voltage ratio (Vout/Vin) applications. .
The ISL8117's low duty cycle (40 nm minimum on-time) feature allows direct step-down conversion from 48V to 1V point of load. By using valley current mode modulation with adaptive slope compensation, the ISL8117 is capable of supporting stable operation over a wide range of input voltage and output voltage combinations without external compensation. System engineers can also use the ISL8117's adjustable frequency of up to 2MHz to optimize power supply cost, size and efficiency.
According to Intersil, using the ISL8117, engineers can design a complete DC/DC buck conversion solution with only 10 components, including MOSFETs and passive components, with up to 98% conversion efficiency and 1.5% output voltage accuracy. The low pin count and easy-to-layout pin structure of the ISL8117 also minimizes the number of overlapping traces, further improving power supply performance.
How do engineers choose a controller when designing an industrial power supply? Which features or parameters should he focus on first? Lokesh Duraiappah responded by saying that many parameters are worth considering, such as input voltage range, output voltage range and so on. From the perspective of the controller, an important factor is the minimum on-time that can be supported, because it is only possible to achieve a large adjustment if the minimum on-time is very low; secondly, it can focus on the gate drive, ie it The maximum number of power MOSFETs that can be driven; the third depends on the ease of use, the default frequency of the search frequency, soft start and the number of pins are satisfactory; the fourth major factor is the switching frequency, which has a very high In the case of the switching frequency, the choice of current wave, efficiency, and inductor size is very large. Of course, the use of reference designs is also very important. After all, no one wants to research and explore a chip from scratch.
But no matter how the technology is improved, efficiency is still a top priority for power products. Lokesh Duraiappah said that reducing quiescent current by improving the product architecture will be one of the future directions. For FET technology and integrated controllers, technology will be further invested to reduce RDS, and the controller manufacturing process will be continuously improved, thereby reducing the board space and improving efficiency.
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