Overview
An embedded product must remember its settings, its calibration and, often, its identity, and it must keep that data for the life of the product. A serial EEPROM is the standard answer, because it keeps the data without power, takes only a few pins and comes in a small package. Microchip offers the I2C 24-series and the SPI 25-series serial EEPROM, and the 24AA02E48 adds a factory-programmed identity. BeiLuo supplies them with genuine traceability and FAE support. This page shows how they cover the data-logging and identity role.
What to Store
A typical embedded product stores the configuration, the calibration, the parameters, a serial number or a MAC address and, for a logger, a set of measurements. The configuration and the calibration are written rarely and read often, the logs are written more often, and the identity is written once at the factory. Keeping them in a serial EEPROM separates the non-volatile data from the firmware, so a firmware change does not touch the settings and a settings change does not touch the firmware.
Choosing the Density and the Bus
Add up the data you must keep and choose a standard density with headroom. The 24LC256 and 25LC256 give 256 Kbit, which covers the configuration, the calibration and a large log, and the 24AA02E48 gives a small 2 Kbit for the settings and the identity. Choose the I2C bus for the fewest pins and the SPI bus for the fastest access, and remember that both families share a common pinout, so the density can grow without a board change.
Endurance and Retention
The Microchip serial EEPROM offers an endurance of about one million write cycles and a data retention of 40 years, so it suits the settings that must last the life of the product. For a logger that writes often, check the endurance against the write rate and use the page write to reduce the number of cycles, and keep a spare page and a check such as a CRC so a power loss during a write does not corrupt the data.
Write Protection
The 24-series and the 25-series provide a write-protect pin and a software data protection scheme, so the critical region can be guarded against an accidental write. Plan the protection region and the unlock sequence before the firmware is written, and use the spare page and the pointer switch for a power-loss-safe update.
Identity and Network Address
A connected product needs a unique identity, and the 24AA02E48 provides a factory-programmed EUI-48 node address at a fixed location, so the host reads a globally unique identity from the same device that stores the settings. This removes the effort of assigning and storing a serial number and fits the small 5-pin package of a compact board. The identity can seed a network address or a license key.
Layout and Verification
Keep the EEPROM close to the host and the decoupling close to the supply pins, keep the I2C or SPI traces short and matched and use a ground plane, because a clean bus is what makes the read and the write reliable across the temperature range and the supply. Verify the design on the bench by writing and reading across the range, by testing the power-loss recovery and by measuring the current in the stand-by mode. Our FAE team can review the layout and the write scheme.
Getting Help
Send your data list, your write rate, your bus and package preference and the environment to our FAE team and we will propose a density and a bus, help plan the write protection and the identity and review the layout. BeiLuo holds mainstream Microchip EEPROM in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, so a data-logging or identity design can move from prototype to production without a supply gap.