Many system designers developing Internet of Things (IoT) devices or low-power RF networks require external memories to help manage data logging and over-the-network or Over-The-Air (OTA) updates. Most of these networks have nodes powered by a battery or by harvested energy, and so require external memory designed with low power usage in mind.
Adesto Technologies offers two families of devices ideally suited to such applications.
The most popular today is the Fusion family of NOR Flash devices, with part numbers in the AT25DFxxx series. They offer a small page size, wide operating-voltage range and deep power-down modes, and provide a serial peripheral interface to a host controller. Available today in densities up to 4Mbits, later in 2016 the Fusion range is forecast to include 8Mbit, 16Mbit and 32Mbit parts. These Flash memories have industry-standard footprints, and a range of package styles including wafer-scale and small-volume dies. Operation over a wide -40°C to 125°C temperature range is a selectable option.
The Fusion family’s wide voltage range of 1.65V to 4.4V provides for the use of various battery chemistries, including lithium polymer, maximising the battery’s capacity usage by supporting operation across its entire discharge curve.
The small Page Erase size of 256bytes is markedly smaller than the minimum erase size of 4kbytes typical for standard Flash devices. As well as freeing capacity for data storage, this also means that the device is ready to accept other commands in around 1.25ms, compared with a 4kbyte block erase operation typically taking between 35ms and 60ms.
Adesto also makes it easier for the controller to manage write and erase operations by allowing the Fusion Flash memory to generate an interrupt when the operation is completed. This allows the controller to go to sleep or to work on other tasks, and to avoid continually polling the memory to check when the operation is completed.
Once any operations are completed the controller can put the Fusion memory into a power-down mode; quiescent current is <200nA.
The Adesto Fusion devices support the security and authentication requirements of IoT devices. Offering 128bytes of One-Time Programmable (OTP) memory which cannot be altered once it has been written, Adesto Flash memories may be used to store random numbers and unique MAC address identifiers. Further options are included to allow the system designer to restrict access to certain areas of memory.
These features make Fusion memories ideal for use in wireless sensors, medical equipment, industrial automation, personal security equipment, building control and smart lighting.
When the power source available to the designer is even more limited, the attributes of Adesto’s Mavriq Conductive Bridge Memory (CBRAMTM) become attractive.
The interface of this non-volatile memory technology is similar to that of an EEPROM device. Mavriq memories with the RM24Cxxx and RM25Cxxx part numbers share a pin-out with their EEPROM equivalents with byte-write and page-write options. CBRAM, however, writes 50 times faster than EEPROM, while drawing around half as much Read current, making it a good alternative to EEPROM when energy consumption is of critical importance.
In addition, the Write current of a CBRAM device is 1mA, which is around five times less than EEPROM. Combining the lower current and the much faster write time, the energy required to write a byte can be as much as 250 times less than an EEPROM uses.
The Mavriq devices are available in densities up to 512kbits, with higher-density parts forecast for release in the second half of 2017. Designers can replace EEPROMs with a CBRAM memory without any software or hardware changes – they provide an easy way to reduce power consumption with very little effort.
There is, however, still more scope to reduce power consumption. Adesto’s Moneta family of CBRAM devices takes advantage of power rails already available on many systems-on-chip, eliminating all non- essential charge pumps and voltage regulators within the memory IC. Suitable for use in wearable and energy-harvesting end-products, the Moneta non-volatile memory range with an SPI bus interface features Read/Write currents of just 10μA, and stand-by current of 35nA.
The Moneta RM3000 parts are available today in densities from 32kbits up to 256kbits, and support various supply voltages. They offer designers a new non-volatile memory option which has far lower power consumption than static RAM.