TME: non-volatile memory chips for IoT devices from Adesto and Everspin
One of the most energy-consuming components in intelligent systems is the non-volatile memory chip used both for storing application code and data. Some interesting chips dedicated exclusively for IoT applications are offered by Adesto and Everspin.
Adesto offers three families of non-volatile memory chips: DataFlash, Fusion and Mavriq.
Thanks to a rather high capacity (up to 64Mbit), DataFlash chips are universal non-volatile memory chips that can be used both for storing large amounts of data and application code. They feature two SRAM buffers (each in the size of a single Flash memory page, i.e. 256B), which means that write operations in case of large amounts of data are conducted noticeably faster. They also feature the commonly used SPI interface, which allows for limiting the number of paths on the board as well as microcontroller inputs used. Thanks to an appropriate architecture, these chips allow for the erase operations to be conducted on the level of a page (256B), a block (2KB), a sector (256KB), or the entire memory. Such flexibility enables more effective management of the available memory, and extends the lifetime of the chip. The chips are energy-efficient, both when active and in idle mode. They offer four modes (work, stand-by, sleep, deep sleep). In the deep sleep mode, the power consumption is ca. 400nA, and while reading at maximum speed (85MHz) it reaches 22mA. Write time for a single data page is 1.5ms.
Fusion chips offer most of the advantages of the DataFlash series described above. They have less memory (4Mbit), but they are also smaller, consume less energy, and are several times cheaper. They can operate in a wider scope of supply voltages (from 1.65V to 4.4V). Reading through the SPI interface can reach the maximum frequency of 104MHz, and the power consumption while reading is ca. 10mA. In the deep sleep mode, the energy consumption is ca. 300nA.
Mavriq chips use memory cells based on the CBRAM (Conductive Bridging RAM) technology. According to the manufacturer, this technology enables write operation 20 times faster than in the Flash technology while using 10 times less power. The architecture of the chip enables random access (read/write) to each memory cell (write time for one byte is 30µs). Supply power consumption is 0.25mA in read, 1.0mA in write, and 1.0µA in standby mode.
An interesting alternative for semiconductor memories can be the MRAM technology (Magnetoresistive RAM) developed by Everspin. This manufacturer offers chips in the sizes from 256kbit to 16Mbit.
MRAM memory is free from numerous issues typical for the Flash technology. There is no need for erasing memory cell contents before re-writing them. Also, there are no limits related to write/read cycles. Additionally, MRAM chips are extremely fast – the time of a single read/write cycle is 35ns. Another advantage is the possibility of storing information for a very long time. The manufacturer declares that the minimum durability of data stored on a media is 20 years.
Depending on the type, the chips are equipped with the following communication interfaces: parallel 8-bit, parallel 16-bit, SPI, and QuadSPI. With the SPI interface, the transfer speed reaches up to 40MHz, whereas in the case of QuadSPI it’s up to 104MHz. All chips are powered by standard CMOS voltages from 3 to 3.6V (for some types, it’s 2.7 to 3.6V). Their power consumption is slightly higher in comparison with the semiconductor memories from Adesto. In read, power supply reaches 60mA, and in write it may reach up to 150mA.