Advantages of FRAM in Automobile Driving Recorder

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Advantages of FRAM in Automobile Driving Recorder [Copy link]

The data in China's car driving recorder should include two parts, one is the real-time data of the car (storing the data before and after the car accident), and the other is the historical data of the car (storing the driving conditions of the car and the driver). I personally think that the real-time data of the car is mainly used to analyze the cause of the accident and the responsibility of the accident. The historical data of the car is used as a reference for accident analysis and the assessment of the running conditions of the car and the driver. The historical data is based on the current real-time data of the car. The entire car driving recorder records the status of 2 input quantities (such as speed and brakes). Others can store 7 switch quantity data (turn signals, doors, etc.) according to the manufacturer's requirements. More advanced ones will also record the temperature of the engine and the status of some other input quantities. Since the data of the driving recorder is so important, the requirements for memory are very high.

It is relatively easy for everyone to choose the memory for storing historical data. Currently, many manufacturers can provide large-capacity Flash and USB flash drives. The most difficult part is the memory for real-time data of the car, because real-time data is more important than historical data, and the data must be saved after power failure (in the event of an accident, the car system may not have power). In order to ensure the accuracy of real-time data, the detection cycle of the input quantity should be as short as possible. According to our current understanding, the national standard requires data to be collected once every 0.2 seconds at most, with 20 seconds as a storage unit. Real-time data needs to store 10 times 20 seconds of data, that is, real-time data needs to store 200 seconds of data. After 200 seconds, the real-time data is sampled and sent to the historical record, and then the real-time data is re-overwritten. It can be seen that the memory requirements for real-time data are very high.

I personally think that the requirements for this storage device are: 1) data needs to be preserved after power failure; 2) a lot of erase and write data, 3) high reliability.

There are currently several ways to achieve this requirement:

1) SRAM+battery+power management IC+EEPROM
2) NVRAM
3) FRAM

The following is a performance comparison of several solutions:

1. SRAM+battery+power management IC+EEPROM

Due to the limitation of the number of erase and write times of EEPROM and FLASH, the detected data cannot be written into them in real time, but can only be stored in SRAM. When a certain time has passed or power failure is detected, the data is written into EEPROM and FLASH. EEPROM stores real-time data, and Flash stores historical data. The characteristics of this solution: the price may be relatively cheap, but the performance is very unreliable. When an accident occurs, the entire system may be out of power. When the system detects power failure, there is no time to write the SRAM data into EEPROM and FLASH. In addition, the environment of the automotive system is relatively complex. We all know that the storage method of SRAM+battery is very unreliable. Therefore, few engineers currently design in this way.

2) NVRAM+Battery Management

There are two types of NVRAM, one is SRAM+battery type, the other is SRAM+EEPROM type. No matter which one, first of all, the price is relatively expensive. As we all know, black boxes are civilian products (trucks over 3.5 tons and private cars with more than 9 people need to be equipped with black boxes). If the price is high, it will not be conducive to promotion.
In addition, in terms of performance, if the NVRAM is SRAM+battery type, there is a risk of battery exhaustion. We all know that NVRAM can only be used for 3-5 years, and the battery may be gone in the future, so it is unreliable to use it to store data.

If the NVRAM is of SRAM+EEPROM type, the principle of this memory is that when working, the MCU operates the SRAM, and after detecting power failure, the data is stored in the EEPROM. In this way, there is also a risk that the data cannot be written in when an accident occurs. Therefore, the data storage is not very reliable.

Before understanding the third solution, let us first understand the basic characteristics of FRAM:

The core technology of Ramtron's ferroelectric memory (FRAM) is ferroelectric crystal material. This special material enables ferroelectric memory products to have the characteristics of both random access memory (RAM) and non-volatile storage products. The main features of the product:

1. High erase and write times, at least 100 billion times.
2. Fast speed, no write waiting time.
3. Low power consumption, read and write current 150Ua, static current less than 1Ua
4. Unlimited read and write times, after more than 100 billion times, FRAM can also be used as SRAM
5. The interface is fully compatible with IIC EEPROM, parallel port SRAM, and ordinary SPI interface EEPROM

3) Storage method of FRAM

Since FRAM has the speed and times of SRAM, and the characteristics of Flash and EEPROM, data can be saved after power failure, and the multifunctional FRAM also has power management function. Therefore, using FRAM can first simplify the system circuit and reduce the system cost. In addition, due to the characteristics of FRAM, the reliability of the system is improved.

At present, some countries with developed automobile industries such as Europe, America, and South Korea use FRAM as their memory for automobile black boxes.