With the rapid development of semiconductor technology, various memories have been introduced one after another, and their performance has been continuously improved. At present, there are mainly the following types of memory: static RAM (SRAM), dynamic RAM (DRAM), EPROM, EEPROM, and FLASH MEMORY. Discuss here a new type of memory integrated by ordinary SRAM, backup battery and corresponding control circuit: non-volatile SRAM (NVSRAM).
In order to solve the data storage problem of SRAM, famous foreign semiconductor companies took the lead in launching NV-SRAM series products that can completely replace SRAM, and similar products have also come out in China. Faced with numerous NVSRAM products, how do users choose high-quality and low-cost products? It is recommended that users choose according to the following performance indicators and prices:
1. Reliability of protected data: It refers to whether NVSRAM is written by mistake on the system and during power-off. This is the most important performance index of NVSRAM, and it is also the most concerned by users and difficult to test at the time of purchase. Although various manufacturers claim that their products are foolproof data protection, in fact, very few actually do this. Most NVSRAM products will lose data when they are used, causing many problems and inconvenience to users. This is mainly due to the following reasons: There is no protection delay when power-on, and data is lost during power-on; when the power is off, the main power supply voltage drops quickly, and the protection circuit cannot quickly switch the power supply of SRAM from the main power supply to the backup battery, or to the SRAM The block selection signal is not timely.
2. Protection voltage: The main purpose of setting the protection voltage is to prevent incorrect writing of data during power-up and power-off. For users, under the premise of completely reliable data protection, the lower the protection voltage, the better.
3. Power-on protection delay: This refers to how long the NV-SRAM can be accessed when the VCC is higher than the protection voltage when the system is powered on. This delay is necessary, because the system may not work normally when VCC is higher than the protection voltage, it may be in a reset state or an uncertain state, and it is very likely to misdetermine NVSRAM. NVSRAM internal circuit with necessary protection delay can effectively prevent miswriting during power-on. Users should pay attention to the delay parameters of the product when using NVSRAM. It is better to test whether NVSRAM can be accessed when the system is working; or add a delay program to the initialization program.
4. Operating temperature range: The protection voltage of some NVSRAM products will vary with temperature. If the system using NV-SRAM requires a large temperature range, you can use the following method to do a simple test: put the NVSRAM in the refrigerator quick-freezing room for about half an hour, and then plug it into the system immediately to test whether the system can read and write NV- normally. SRAM.
5. Access speed: All kinds of NV-SRAM products are marked with access speed, and users can choose according to their application system requirements.
6. Power consumption and service life: Foreign products all use low-power chips, the internal control circuit current is less than 1mA when the system is working normally, and the system switches to battery power when the system is powered off. The current is only about 100nA at this time. NV-SRAM all use lithium batteries as a backup power source. Due to the low self-consumption of lithium batteries, the service life of NV-SRAM is generally about ten years.
7. Price: Generally speaking, foreign products are expensive and domestic products are cheap. However, for chips that will lose data, even if the price is cheaper, users are advised not to choose them.