Shengbang Microelectronics' monitoring product innovation matrix protects system security

The instability of the external world has brought various problems and challenges to circuit system designers. In order for electronic systems to detect system errors that have occurred or are about to occur, and to recover safely from fault conditions with no or minimal human intervention, to minimize the impact of such faults, and to ensure that the system can start correctly every time, designers have launched a series of monitoring chip products with different characteristics.

Taking the first generation reset monitoring products 706 and 809, which are most familiar to engineers, as an example, the highly integrated voltage monitoring, reset operation, watchdog timer, manual reset, power failure comparator and other functions may seem ordinary, but for many applications, these basic and easy-to-implement functions play a vital role because they bring higher reliability and accuracy to the system.

The 706 and 809 were originally designed to monitor the working status of microcontrollers (MCUs)/microprocessors (MPUs). Today, reset monitoring products have developed into the most complex and diverse category of all analog products, but surprisingly, these products are rarely used to monitor MCUs. So, does the necessity of external reset monitoring circuits depend on the reliability of the MCU's built-in reset circuits? Why do the applications of reset monitoring products continue to exist and change?

We first need to answer and clarify the above questions.

In fact, the microprocessor monitoring circuit is a rare circuit that has not changed much in function since its appearance. The first 706 has been on the market since 1993. The 706 produced by different manufacturers has maintained the original concept, function and performance except for the reduction in power consumption. At present, almost all the built-in reset monitoring circuits of single-chip microcomputers are well-designed independent units, and there is no problem of unreliable built-in reset circuits of single-chip microcomputers. Therefore, there is no need for an external reset monitoring circuit under single system operating conditions.

However, when there are many operating conditions that need to be monitored in the system application, it is necessary to consider using an external reset monitoring chip. For example, the external memory may not be on the same power rail as the MCU, and some input and output units may be on another power rail, etc. Any local problem will cause the system to be abnormal or even crash, so a reset monitoring circuit is needed to monitor multiple operating conditions of the system and assist or rely on a reliable MCU to ensure the normal operation of the system. In this way, the reset monitoring circuit is not only used to monitor the MCU, and it neither repeats nor conflicts with the built-in reset circuit of the MCU.

In a nutshell, a simple, self-contained embedded microprocessor can do without an external monitoring circuit, but applications that require external cooperation and coordination still rely on the monitoring circuit to coordinate and dispatch. If the internal circuit of the microprocessor can work at a lower voltage, the low-voltage working characteristic will not be reserved for the monitoring part. "A modern luxury car must have a handbrake, and an advanced airplane must be manually braked." Therefore, the microprocessor monitoring circuit in a complex system has taken on a new task: to force the microprocessor to reset as soon as possible at the beginning of power-on, and then release the force until the rest of the system works normally.

The second common misunderstanding is related to reset delay. Even for a slow-paced MCU, the startup reset process will not exceed hundreds of microseconds. The reset time in a real system is not to reset the MCU internally, but to allow the controlled part to fully release stress and return to the initial state, so that the entire system can be effectively reset. On the other hand, in actual application scenarios, user needs, such as ultra-low standby power consumption, ultra-small package, adjustable dog feeding/reset time, graded timing, voltage window/high-voltage bus monitoring, etc., vary greatly; at the same time, due to the increasing complexity of system design, designers hope that "even if a problem occurs, the system can work or stop safely", and need to balance multiple factors such as product performance, size, package type and price. Such complex influencing factors often make it difficult to make a decision. Knowing this, you can understand why the application of reset monitoring products continues to exist and change.

As a result, monitoring chip products have opened the curtain on the transition from traditional single-category monitoring to system-level monitoring .

The so-called system-level monitoring refers to all monitoring parts used to ensure system operation outside of the core business functions. In the concept of system-level monitoring, in addition to the most common voltage and current range monitoring and the very common but usually unrecognized time monitoring, there are also frequency monitoring, temperature monitoring, humidity monitoring, condensation monitoring, proximity monitoring, abnormal electromagnetic monitoring, leakage monitoring, salt spray monitoring, field strength monitoring and heartbeat monitoring. Single voltage monitoring is divided into low voltage, high voltage, AC voltage and a variety of products with different packaging specifications. The concept of system control usually refers to power sequencing and function sequence startup, extending to the management of load switches and hot-swap switches and hot-integrated switches that need to be configured. Actuator drivers (such as motor drivers and solenoid drivers) and power distribution/modulation circuits are not system control elements.

Since its establishment, Shengbang Microelectronics has focused on high-reliability applications and complex system applications. The genes of reliability and system are imprinted in all of Shengbang Microelectronics' products. Relying on the evolution of CMOS technology and design, the company has fully upgraded and updated its reset and monitoring products. Currently, the entire series of products are μA and sub-μA level products, and the product specifications and packaging can cover most European, American, Japanese and Korean products.

The 1μA operating current means that a 1kΩ damping resistor in series on the power path will only result in a 1mV voltage change. This shift in the entire product line toward low power consumption not only meets the needs of battery-powered systems and energy storage power supply systems, but also brings considerable convenience to simplifying the monitoring voltage filtering and monitoring circuit self-protection in conventional power supply systems.

As mentioned above, there are many types of reset monitoring circuits. Voltage monitoring and reset control alone need to be described in six dimensions: voltage range, input form, output type, delay type, working environment adaptability, and package type. Traditionally, it is impossible to prepare a complete reset monitoring product by drawing a table and filling in the blanks. For this reason, Shengbang Microelectronics creatively proposed an "innovation matrix" product development approach, that is, to build a large number of certified unit circuits, also known as design components (Building Block), and on this basis, quickly develop and fill in the required varieties according to application needs, so as to achieve complete coverage.

Shengbang Microelectronics' existing reset monitoring products fully cover the market demand. From SGM820 and SGM821 that meet the system standby power consumption requirements and adjustable feeding time requirements of portable and ultra-long standby products, to SGM892, SGM895, SGM826 and SGM822 that meet the requirements of ultra-small package, hierarchical timing, high input voltage and multi-rail hierarchical sorting, to SGM829, SGM836 and SGM89X series that meet the reset time, adjustable requirements and low detection voltage requirements, we strive to protect customer system security in all aspects.

Figures 1 to 3 show some of Shengbang Microelectronics' monitoring products with reset output, watchdog timer and voltage monitoring functions.

Figure 1 Overview of existing single reset function devices

Figure 2 Overview of existing reset devices with watchdog function

Figure 3 Overview of existing reset devices with voltage monitoring function

The SGM706 microprocessor monitoring circuit is a classic product of Shengbang Microelectronics, with complete functions such as reset monitoring, independent watchdog monitoring, watchdog trigger start, and low-level manual reset input (MR). Among them, the reset output maintains operation with V _CC as low as 1V; once activated, if the watchdog input is not switched within 1.6s, a reset pulse is output (before the SGM706 watchdog function is activated, the system has sufficient time to complete time-consuming tasks such as initialization). In addition, there is a 1.25V threshold detector for power failure warning, low battery detection or monitoring of additional power supplies. The upgraded product SGM706B of SGM706 has lower standby power consumption.

Another representative product is the SGM821 heartbeat generator circuit. The difference between the heartbeat generator and the watchdog is that the watchdog passively waits for the MCU to feed the dog signal, and resets the system if there is no feeding signal; the heartbeat generator actively times and sends a signal to wake up the MCU after the predetermined time is reached (in a system that sleeps for a long time, the main MCU will shut down most of its own functions including the built-in watchdog). The heartbeat circuit is used to ensure that the system can be reliably awakened from a deep sleep state. SGM821 can also be used as a watchdog, and the feeding time is adjustable in a large range of 100ms-7200s; the feeding action "tells" the heartbeat generator that the system is already working and there is no need to wake up or reset the system. In addition, its typical standby power consumption is 35nA and the typical timing accuracy is 1%. It is very suitable for applications with long-term dormancy and timing acquisition/collection of signals (such as in-vehicle, Internet of Things, etc.). This is in stark contrast to our other product SGM800; SGM800 achieves timing in the ms-s time range through the capacitor charging process, and does not have the heartbeat generator's feeding and wake-up functions. The heartbeat circuit can be used to wake up the system in advance to prepare for the scheduled task, and can also be used to trigger remedial measures or reset the system when the system timing is missed.

It should be emphasized that monitoring products play a role in ensuring the operation of the system. They must work outside the boundaries of the system's operating conditions and be more reliable than the system. Reset is part of system control and serves the system. One of its important characteristics is that it must output reset clearly before other circuits work to prevent the system from working uncontrollably when its state cannot be guaranteed. After the system is over-voltage, it also relies on it to ensure that the system is in a static state in order to improve its over-voltage resistance.

Providing as much product coverage as possible and building a more complete monitoring product ecosystem are the responsibilities and missions that Shengbang Microelectronics has given itself. If there are multiple conditions that need to be monitored, whether it is a single threshold or multiple thresholds, delay or no delay, single monitoring or combined sorting, almost any combination of conditions can find a suitable model from Shengbang Microelectronics' existing products. Even if there is no suitable model for the time being, there is a high probability that a new model can be quickly developed using existing modules.

Users need high-quality analog design components, as well as a wealth of solutions and subsystems created on this basis. Therefore, on this road of rapid product iteration and exponential growth, Shengbang Microelectronics will not stop innovating. New products represented by 12V/24V/48V high-voltage bus monitoring applications and window voltage monitoring applications are under development, which will provide appropriate functional combinations for all applications in a more flexible way.