High reliability system design includes using fault-tolerant design methods and selection of suitable components to meet the expected environmental conditions and meet standard requirements.
This article specializes to explore a semiconductor solution for high reliability power supplies, which provides redundant, circuit protection, and remote system management. This article will highlight, how to improve the improvement of semiconductor technology and how new security features simplify design, and improve the reliability of components.
High reliability power system requirements
In the ideal world, high reliability systems should be designed to avoid single-point failure, and there is a way to isolate the failure in the case of maintaining operation (but perhaps at a reduced performance level). High reliability systems should also be able to suppress faults to avoid failures to downstream or upstream electronic components.
Built-in redundancy is a solution that can be taken in an alternate pattern with a parallel circuit to actively share or wait for an alternate pattern before the failure occurs. In each built-in redundancy, it requires additional circuit overhead in failure detection and management, which increases total complexity and cost. Some systems have also established different parallel circuits to increase diversity to avoid this risk of the same fault mechanism, and some flight control systems do this.
Increasing system complexity has caused a greater burden on power performance, so high conversion efficiency and good heat management become critical, because the junction temperature is 10 ° C, the IC life is approximately half. As we will see, now new features rich power ICs and dedicated power management functions have enhanced protection for IC itself and its surrounding systems.
Power supply regulator security function
The current limitation of the voltage regulator is getting more accurate, the form is increasingly complex to avoid excessive output current damage the device itself or downstream components. The internal protection circuit is also quite common, including battery reverse protection, current limitation, heat limit, and current reverse protection.
The LTC7801 DC / DC switch controller is a product instance that improves process technology and security functions. The device can safely withstand the input voltage of up to 150V and provide a protection function to prohibit switching when the input voltage is raised above the programmable operation range. This function simplifies the input power transient protection circuit, reducing the number of components and reduces the size of the solution. The overvoltage comparator that provides protection against voltage overshoot can also protect the output, and the retrieval current limiter can control power consumption in the case of overcurrent and short-circuit faults.
Figure 1: LTC7801 high pressure buck DC / DC controller
The wide pin interval can avoid dangerous arc between adjacent high pressure and low-voltage pins, by providing such packaging selection, also enhances the security of physical packaging. The breakdown voltage decreases as the air pressure is lowered, and therefore the aircraft applications of abnormal pressure can be selected, which provides the same functions and performance as LTC7801, but providing a package selection with 0.68 mm double pin interval. In addition, some products that have a lead-out feet that conform to the so-called FMEA (fail mode and influence analysis), such as a fault-tolerant LT3007 linear regulator, in such extraction feet, if adjacent pin is short When or a pin is floated, the output is maintained or lower than the adjustment voltage.
Control multiple input power supplies
There is a power supply and a redundant backup power supply at the same time may have an external auxiliary power supply require an arbitration system to determine which power is priority and monitors the status of these power. In addition, it is also necessary to protect the system to prevent cross-conduction and reverse feed when power switching. SLD ICs such as LTC4417 provide a solution that verifies the user-defined power threshold for each input, and automatically selects the power supply.
Another approach is to support the load of two simultaneous input power supplies, thus improving the reliability by reducing the burden of each power source. If each power source is properly adjusted, it is possible to support full load requirements, then this method can also Protection is provided when a power is faulty. In the past, a simple but efficient diode "combined" circuit may always be used, but this circuit requires that each power supply is equipped with active control to balance the load. Figure 2 shows how to implement this control now with a single chip solution. The LTC4370 is a bicyclic controller with reverse isolation, preventing a power supply failure causes the entire power system downtime.
Figure 2: LTC4370 dual redundant power supply
Transient and circuit protection
Military and avionics must meet transient protection specifications, such as MIL-STD-1275 (vehicles) and MIL-STD-704 / DO-16 (aircraft). However, people want any high reliability system to provide protection for voltage surges, spikes and ripples, and some products provide such protection functions, such as LT4364.
In addition, there are a variety of circuit protection functions, including LTC4368 products. The LTC4368 is a 100V bidirectional circuit breaker that is too high, too low or even negative, and provides protection against forward and reverse overcurrent faults.
Figure 3: LTC4368 two-way circuit breaker providing protection function
In these examples, we can observe how new products with increasingly complex protection and security functions simplify the application circuit design and reduce solution size.
Digital power system management
The analog power adjustment has its own advantage, and digital control is performed by I2C-based PMBUS interface to support power system remote management. There is also its own advantage, and new products are combining these two advantages. The telemetry and diagnostic data can be used to monitor load conditions, read chip temperature and perform fine-tuning and margin control at very high accuracy, thus maximizing system stability, efficiency, and reliability.
One of the interested issues of digital power management is the complexity of the software. However, the LTC3815 performs a simplified PMBus "Lite" command set, no in-chip non-volatile memory or microcontroller, which provides simultaneous design The benefits of digital control and monitoring.
As mentioned earlier, good calorie control is very important for reliability, and the LTC3815 provides two-level overheating threshold and two-level responses. When the internal chip temperature exceeds 150 ° C, the overheating state is marked on the PMBUS, and the Alert pin pulls low to issue an alert to the PMBus master. If the temperature continues to rise and exceeds 170 ° C, then the LTC 3815 turns off all circuits, including the output adjustment circuit until the overheating state is cleared.
Such systems that report their status provide opportunities for changing maintenance, that is, transition from time-based maintenance arrangements to state-based maintenance, and may highlight performance degradation problems before system failure.
Isolation system
High reliability power systems typically include an isolation barrier to protect the power bus from the downstream line to replace the unit failure. In addition, the number of increasing sensors and actuators is also pushing for smaller, partially isolated power supplies, and data interfaces aimed at reducing noise sensing problems derived from ground loops and common mode interference. There is now a complete current isolation BGA module solution to simplify design and improve reliability. The LTM9100 isolation switch controller is an integrated solution for controlling, protecting and monitoring high voltage power supplies up to 1000VDC. A 5kVRMS electrical isolation barrier isolates the digital interface and switch controller to drive an external N-channel MOSFET or IGBT switch. The load current, bus voltage and temperature can be isolated digital measurements via the I2C / SMBUS interface, thereby achieving power and energy monitoring of high voltage bus.
Figure 4: LTM9100 isolation switch controller with telemetry function
Component selection
Most of this article is specifically used to explore new features that simplify high reliability power supply design, or protect the product functions of the device for faults or crude use. However, it is essential that do not ignore the importance of component quality to select the importance of the correct component level for expected environmental conditions. For example, the military plastic packaging grade device for ADI provides 100% test and guaranteed performance (within -55 ° C to + 125 ° C temperature range), eliminating components in applications that are expected to exist very harsh conditions. Perform expensive secondary screening or feature analysis.
in conclusion
With user programmable characteristics, more fine and complex sheet protection mechanisms and reduced overall solutions have higher integration, which has made high-reliability power supply simplified. Digital power system management provides a way to remotely monitor and control power systems and further improve efficiency and reliability. Finally, choose a reputable supplier's correct component level will reduce the possibility of quality and reliability issues.
Original link: https://www.eeboard.com/news/ic-5/5/
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Original link: https://www.eeboard.com/news/intel-87/
Search for the panel network, pay attention, daily update development board, intelligent hardware, open source hardware, activity and other information can make you master. Recommended attention!
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