Interest in wearables and IoT applications continues to grow. Mobile devices keep getting smaller and their service life and standby times longer. These phenomena are also reflected in the development of digital memory modules: Performance, storage density, speed, and service life are all increasing while power consumption is falling. Due to their reduced size and relatively low operating current, flash memories and EEPROMs (electrically erasable programmable read-only memories) are now the most commonly used memory chips for IoT, wearables, etc.
EEPROMs are semiconductor memories consisting of interconnected field-effect transistors with floating gates (Fig. 1). They are extremely small, can be operated at low voltages, and consume very little power. Further, they enable multi-byte operation and have a reduced number of pins.
The memories are programmed by charging the floating gate of the transistor (Fig. 2). The written data are represented by a bit pattern of charged and uncharged gates. They can be read as often as required via the drain-source connections of the transistors, with the normal operating voltage well below the programming voltage during the actual reading process.
EEPROMs are non-volatile memory modules. The typical retention period of the stored data is upwards of ten years. However, it takes much longer to program an EEPROM than a flash memory, since the data are written or erased byte by byte and not as whole blocks of data. The advantage: Developers can focus their full attention on certain parts if need be. Only an external power supply is required, as the higher voltage necessary for programming/erasing is generated internally. Maximum endurance cycles typically vary between 10,000 and 1,000,000.
EEPROMs are used wherever smaller data volumes need to be stored and kept available for greater intervals over longer periods of time. In addition to call number memories in phones, they can also be found in memory cards and microcontrollers, for instance. Other applications include SSDs, BIOS (basic input/output system) in computers, or RAM memory modules, where they retain configuration data or parameters required for operation.
Serial and parallel interface types
EEPROMs are available in two classes. Models with serial access are very small and cheap, and account for roughly 90% of the total EEPROM market. They are predominantly found in standard applications, since, unlike parallel EEPROMs, they are slower and have a lower storage density, typically of between 256 bits and 256 kbits.
In contrast, parallel modules have a higher storage density (≥256 kbits). They are generally faster and guarantee a long service life and extensive reliability. Unlike serial EEPROMs, a higher pin count of 28 or more is required, making them somewhat larger – usually too large for the ever-smaller end products.
Making a decision between serial and parallel modules is therefore a trade-off between cost, available space, and memory density. However, the operating temperature and operating voltage as well as the required minimum or maximum voltage also need to be taken into account when selecting the right memory.
Generally speaking, EEPROMs support SPI, I2C, and Microwire interfaces. Data throughput, availability, and power consumption of the system are the crucial points here. SPI enables speeds of up to 20 MB/s and is the preferred solution for high-speed applications, but requires four wires for communication instead of just two like I2C (with 400 kB/s to 1 MB/s). When using I2C, fewer MCU ports are required as multiple EEPROMs can be connected to the same bus. Microwire is slower than SPI and only available with smaller memory capacities. This solution also requires four wires.
Memory modules for PC main memories
Computers perform a self-test each time they are switched on. This includes automatic detection and configuration of the installed hardware. Serial presence detect (SPD) is information stored in an EEPROM on an SDRAM memory module that tells the BIOS about the module’s capacity, data width, speed, voltage, etc. The BIOS uses this information to configure the memory properly for maximum reliability and performance. Correct communication between the processor and memory would not be possible without SPD.
A dual inline memory module (DIMM) is a memory chip equipped with a certain type of SDRAM memory module and serves as the main memory in PCs, servers, and other devices. DIMMs consist of one or several random access memory (RAM) chips and a small circuit board that connects them to the computer motherboard. The data bus is based on 64 bits.
An extensive range of DIMMs is available. All of them measure the same length but are not compatible with each other. The modules differ in terms of their operating voltage, number of contacts, and coding notches. They are designed to prevent modules of different memory types (SDR, DDR, DDR2, DDR3, etc.; see Table 1) being accidentally inserted into the wrong slot.
DDR SDRAM and the variants DDR2, DDR3, DDR4
The abbreviation DDR SDRAM stands for double data rate synchronous dynamic random access memory. The semiconductor memory is used not only in computers but also in motor vehicles, networks, medical technology, and consumer electronics. The variants DDR, DDR2, DDR3, and DDR4 SDRAM differ in terms of their data transfer rates, clock cycles, and number of contacts.
Compared to conventional SDRAMs, the transfer rate of the memory is much higher. This is possible due to the double data rate (DDR): For example, when transmitting data, both the rising and the falling edge of the clock signal are used for data transmission. This basically doubles the band width.
Further, each SDRAM memory module has a digital data sheet to ensure the motherboard can carry out the necessary memory controller settings. It is saved in the SPD EEPROM and read by the BIOS. The information contained therein is elementary for configuration of the memory controller.
Ultra-low-power EEPROMs for wearables and other IoT applications
The demand for EEPROMs is increasing all the time, especially in the field of IoT applications. In this case, small devices with small batteries that offer the longest possible standby time and service life are crucial. This obviously requires low power consumption and low operating voltage. The solution is provided by compact ultra-low-power EEPROMs.
Giantec Semiconductor offers a wide range of reliable products. With more than three billion EEPROMs sold to date, the firm ranks third globally, and first in Asia. The reason for this level of success is the high-quality models. They offer a standard standby current of Isb < 200 nA, and the maximum working current is only 300 µA. The battery life can be further enhanced by switching off the EEPROMs when they are not being used by the PIO (Programmable I/O). Giantec offers EEPROMs for I2C, SPI, and Microwire interfaces as well as in all standard packages such as PDIP, SOP8, MSOP8, DFN, and WLCSP.
The entire EEPROM GT34 line from Giantec supports DDR2, DDR3, and DDR4 SDRAM. DDR3 and DDR4 also come with Intel certification for DIMM applications. The highly reliable SPD/TS (TS: temperature sensor) product line for DIMMs (Table 2) is available in various package types and with operating voltages ranging from 1.7 to 5.5 V. The EEPROMs offer excellent endurance of one million cycles and data retention of 100 years.
As the sole distributor of Giantec worldwide, Rutronik provides its customers with the best advice and aid in selecting the right product for the respective application from the myriad of options available.
For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.
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