[Introduction]Infineon’s direct tire pressure sensor chip SP40+ is the mainstream chip on the market. Its average quiescent current is only about 245nA, which can ensure the normal operation of the tire pressure sensor module on the vehicle for ten years; its automatic positioning algorithm function, even when the vehicle is repaired and replaced with the wrong tire, the system can still automatically identify the tire pressure sensor position and update on the screen.
Up to now, Infineon has delivered more than 700 million tire pressure sensor chips, and the defect rate is far less than 1ppm.
Infineon’s direct tire pressure sensor chip SP40+ is the mainstream chip on the market. Its average quiescent current is only about 245nA, which can ensure the normal operation of the tire pressure sensor module on the vehicle for ten years; its automatic positioning algorithm function, even when the vehicle is repaired and replaced with the wrong tire, the system can still automatically identify the tire pressure sensor position and update on the screen.
At the end of 2017, the mandatory national standard for the tire pressure monitoring system (TPMS) was introduced. All new cars purchased will be equipped with the tire pressure monitoring system when they leave the factory. The standard will be officially implemented on January 1, 2020.
Why did China introduce this mandatory regulation after Europe and the United States? According to the statistics of the traffic management department, at present, more than 70% of traffic accidents on highways in my country are caused by tire blowouts. Once the front tire blows out, the fatality rate of rollover accidents is nearly 100%. The main reason for a flat tire is due to under-inflated tires, so if the driver can be reminded to slow down in time when the tire is under-inflated, it will be very direct and beneficial to avoid accidents.
The role and function of the direct tire pressure monitoring system is exactly this. It can monitor the current tire pressure status of the four tires in real time. Once an abnormality occurs, an alarm will be issued in time to remind the driver. Infineon can provide a complete set of system solutions for customers to use. The system block diagram is as follows:
The tire pressure information and alarm information displayed by the system on the vehicle instrument are shown in the following figure:
Infineon direct tire pressure monitoring product roadmap
Infineon has been deeply involved in the field of direct tire pressure monitoring systems for many years, and is committed to developing the most advanced chips. At the same time, it is constantly updating and iterating and optimizing performance. It also pays attention to the user’s cost of use and helps customers reduce the cost of use of the entire system. Since 2008, Infineon has launched several generations of TPMS, with continuous product updates and a very clear development plan:
Detailed explanation of key advantages of SP40+
Infineon’s direct tire pressure sensor chip SP40+ is the most mainstream chip on the market, so what kind of chip is it? What are the features and advantages? Let’s talk about the functions that the chip contains necessary for TPMS applications, as shown in the following figure:
SP40+ supports two pressure measurement ranges, 100~500kPa and 100~900kPa, to suit different car size types. The chip only needs very few peripheral devices to realize all the functions mentioned above. The specific application schematic diagram is shown in the following figure:
As a technology and quality leader, Infineon SP40+ has three major advantages and features: low power consumption, automatic positioning algorithm, and high quality.
1 Low power consumption
The average quiescent current of the SP40+ is about 245nA, which can guarantee the normal operation of the tire pressure sensor module on the vehicle for ten years. Low quiescent current is one of the important reasons why it has such a long service life. However, this is not enough. This chip has a very meticulous state machine that works continuously. There are a total of six states in the cycle. It operates in a software-defined manner, as shown in the following figure:
In each state, each module inside the chip performs its own duties, because the power consumption and function of each module are different, so the more modules work, the more current consumption will be brought, such as: In the Run state, the CPU and the 12MHZ main clock are in normal operation, and all other modules can be woken up and activated as needed. The average power consumption at this time is about 0.85mA@25℃; in the RF-transmission state, the power The maximum power consumption is about 5.7mA@25℃; in the Power-down state, only the wake-up controller and the low-frequency receiver are still working, and the average power consumption at this time is about 245nA@ About 25℃; in the idle state (Idle state), the application program is not executed, but the CPU is still working, the power consumption at this time is about 280uA@25℃; in the deep idle state (Deep idle state), it is It saves more power than the idle state, and the power consumption is about 2.1uA@25℃. In short, when a certain or certain modules are required to run, these modules are called to start, and when they are not needed, they are put to sleep.
In addition, SP40+ also has a built-in radio frequency (RF) transmit state machine, also known as RF transmit controller, it is only used in FSM mode, its purpose is to reduce the overall power consumption during the RF transmit process, put a simple and Repeated operations are handed over to a less smart but more power-efficient module to reduce the overall power consumption during RF transmission. Next, we explain in detail how it helps the system save power consumption. In the TPMS application, the RF packet contains several frames (depending on the customer’s own definition). When these frames are repeatedly sent, in order to ensure the receiving success rate of the receiving end, the RF transmitter is not activated between these frames. At the same time, a The timer will run continuously to time the RF transmit inter-frame. Of course, in order to complete the specified inter-frame timing task, the CPU is definitely capable, but the current required for the CPU to run is relatively high (0.85mA@25°C), and when the RF transmit state machine is used to complete the inter-frame timing, the current consumption Reduced to 2.1uA@25℃, reducing the current consumption during idle time between frames reduces the current consumption during the entire RF transmission. Of course, the SP40+ CPU can still handle other tasks during the activation or operation of the RF transmission state machine, and the transition between the CPU control and the state machine can be coordinated in the application software.
Based on the above functions and features, the SP40+ achieves low power consumption, which allows end users to save a lot of trouble and cost without frequent replacement of sensors.
2 with automatic positioning algorithm
What is automatic targeting? The automatic positioning of the tire pressure monitoring system is actually that when the vehicle is running, it can automatically identify which wheel the signals of the four tire pressure sensors come from, so that the tire pressure and temperature information can be accurately displayed on the screen. This function is mainly used by the end user when the vehicle is being repaired and maintained, if the front and rear wheels are actively swapped or the wheel is in the wrong position or even a new tire pressure sensor is replaced, the user does not need to re-diagnose the OBD to change the tire pressure. The monitoring system has saved the location information, just drive the vehicle for a period of time, the system will automatically identify the location information of the new tire pressure sensor and update it on the screen, which reduces the time for after-sales maintenance and repairs, and greatly facilitates users and 4S maintenance. shop. The SP40+ chip integrates the automatic positioning software algorithm and is provided free of charge to customers using the chip. What is the principle of this algorithm? Please refer to the picture below:
It uses the tire pressure sensor to send RF signals regularly, and at the same time, the vehicle ABS module will also send the information of the number of teeth of the wheel rotation in real time. When the number of teeth of the wheel reaches a certain value, the tire pressure sensor of the corresponding wheel also At the same time, the RF signal will be sent out at that position. As long as the precise values of the two signals can be counted, which tire pressure sensor corresponds to which wheel position can be calculated. This automatic positioning algorithm integrated by Infineon is called angular position sensing (time and phase method). Through the tire pressure sensor to collect a certain amount of acceleration information in each rotation cycle, an estimated wheel rotation frequency can be obtained, and then an estimated wheel rotation frequency can be obtained. These sampled data are subjected to discrete Fourier transform to extract the precise rotational frequency. The patented principle is shown in the following figure:
3 high quality
The last point, but also a very important point, is high-quality features. Up to now, Infineon has delivered more than 700 million tire pressure sensor chips, and the defect rate is far less than 1ppm, which is enough to show that Infineon tires Ultra-high quality and performance of pressure sensor products.
Source: Infineon, Original: Li Hui
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