Non-volatile memories from MICROCHIP
The demand for non-volatile memories originates mainly from the constant development of portable devices featuring an increasing amount of memory. These are mainly video cameras, smartphones, tablets, or photo cameras. This increasing market demand forced the continuous development of the non-volatile memory manufacturing technologies.
The idea behind non-volatile memories is to maintain data when the device is not powered. Nonetheless, power is required for saving and reading the data.
Both Microchip, and the recently acquired Atmel have extensive experience in the field of manufacturing non-volatile memories. Their manufacturing process is conducted in their own silicon factories. To maintain the highest quality level, advanced testing procedures are used. This manufacturer’s portfolio also includes memories with AEC-Q100 qualification, which means they are approved for automotive applications. It is also worth mentioning that the memories that have already been marketed are still in production.
EEPROM memories (Electrically Erasable Programmable Read Only Memory) are also non-volatile memories. Solutions of this type are usually used in applications requiring reprogrammable ROM memories, especially in connection with storing system configuration data.
In terms of the interface, EEPROM memories can feature serial or parallel interface. Serial memories (24xx series with I2C interface, 25xx series with SPI interface, 93xx series with Microwire interface) usually come in DIP or SOIC packages. Their capacity reaches dozens of kB. Because of the serial interface, compact size, and low energy consumption level, they are commonly used for storing information regarding serial numbers or configuration and production data. There are also serial memories with a pre-programmed 48- or 64-bit unique address, which can be used as a MAC address of the device.
Parallel memories are available in the 28xx series. Note that in terms of reading functionality and pins, these are compatible with the 27xxx series EEPROM memories.
The scope of applications of EEPROM memories includes mainly industrial electronics – measurement devices and control systems, security and alarm systems, sensors, or battery chargers. They can also be found in IoT devices. EEPROM memories are also used in medical devices and in automotive industry. What is more, EEPROM memories are commonly applied in consumer electronics, i.e. in personal computers or Home Appliances.
In terms of ensuring production continuity of various devices, Microchip support in the area of maintaining the production of EEPROM memories manufactured with the use of legacy technologies (1.2um - 0.7 - 0.5 - 0.4 - 0.25 - 0.18 - 0.13um) plays a crucial role.
Development directions for EEPROM memories include primarily lower power consumption and supporting new interfaces. Here, the UNI/O asynchronous serial bus created by Microchip in 2008 (11xx series) should be mentioned. It is based on the Single Connection I/O (SCIO) data line, resulting in 3-pin packages, which makes it possible to use the SOT23 or TO92 packages. The latest solutions are memories with the Single-Wire interface (21CS series), where the system is powered by a bidirectional data line, reducing the number of pins to two (SI/O + GND).
Non-volatile FLASH memories offer shorter saving and reading times in comparison with EEPROM memories, but this comes at the cost of inability to read or save individual bytes. Here, saving and reading is realised on larger parts of memory, the so-called pages (128/256 bytes). Flash memories offered by Microchip feature parallel interface (SST39 series) or series interface (SPI in the SST25 series or SQI in the SST26 series). Important parameters of Flash memories are: capacity (e.g. 4 Mbit), operating frequency (e.g. 40MHz), operating voltage (e.g. 2.3–3.6V), package type (e.g. TDFN8), mounting type (e.g. SMD), and operating temperature (e.g. -40 – 85°C).
The SuperFlash technology ensures lower power consumption and very short data erasure times. The SQI interface guarantees fast data transmission while using the minimum number of pins.
EERAM is a combination of fast SRAM memory (Static Random-Access Memory) and non-volatile EEPROM memory, storing a backup copy of the SRAM memory (I2C, 47x series). This combination means that in case of power supply issues cached content can be restored from a backup. Therefore, EERAM is based on an external capacitor, which serves as the source of backup power for the time needed for copying memory contents.
It is worth mentioning that this is similar to the NVSRAM memory (Non-volatile Static Random-Access Memory – 23XX series), which also offers the functionality of maintaining the memory state. However, to operate correctly, they need an additional source of power – a battery, which is not required in the case of EERAM memory. This impacts the manufacturing cost of the device.
What’s important, the number of data writing and reading operations is unlimited. Depending on the needs of a particular application, EERAM memory with the capacity of 4kb or 16kb is used.
During operation, internal logic is responsible for monitoring the status of power supply in real-time. As a result, any dips and interruptions of power are detected, taking into consideration the approved threshold (Vtrip). If any of these statuses is detected, the system initiates copying the contents of SRAM memory to EEPROM memory. An external capacitor connected to the Vcap pin of the IC plays a crucial role here. When the voltage is restored above the Vtrip level, the contents of EEPROM memory is copied to SRAM memory. It should be emphasized that the contents of SRAM memory can be restored at any time using a software trigger.
To sum up, EERAM memories are perfectly adapted to be used in applications requiring fast and frequent updates of memory cells, while ensuring that data stored there is safe in case of any interruptions of supply voltage. This means they are perfect for measurement electronics (electricity meters, gas meters, liquid meters), industrial and consumer electronics (POS terminals, info kiosks, printers), and automotive industry (data loggers, sensors).