AT24C / 24Cxx EEPROM Shortage or Cost-Down? Second-Sourcing with FMD FT24C (Mind the Page Size)
The 24Cxx I²C EEPROM is a multi-vendor de-facto standard, and FMD (Fremont Micro Devices) FT24C is a pin- and protocol-compatible same-density second source (1K–1Mbit, 1.8–5.5V). But check the page size before swapping — at 1K/2K density FMD uses a 16-byte page while Atmel AT24C01/02 uses 8 bytes, and getting it wrong overwrites data. Here is how to migrate safely.
24Cxx is a de-facto-standard I²C EEPROM
The 24Cxx is a multi-vendor 2-wire (I²C) serial-EEPROM naming family, with densities from 24C01 (1Kbit) to 24C512 (512Kbit) and even 1Mbit, made by Atmel/Microchip (AT24C / 24LC), ST (M24C), ON Semi (CAT24C), Rohm (BR24G), FMD (FT24C) and more — all highly aligned in pinout, I²C address and read/write protocol; it is an industry de-facto standard. Because it is a multi-vendor common part, switching to another vendor’s same-density second source when one goes short or you want a cost-down is relatively simple — but “relatively simple” is not “swap blindly”; a few things must be checked first.
FMD FT24C: a pin- and protocol-compatible second source
FMD’s (Fremont Micro Devices) FT24C series is exactly such a pin- and protocol-compatible 24Cxx second source, with the full density range from FT24C01A (1Kbit) up to FT24C1024A (1Mbit); the whole series is wide-Vcc 1.8V–5.5V (note: 1.8V minimum, not 1.7V), uses the standard 1010 control code plus A2/A1/A0 for the I²C device address (the 7-bit addresses 0x50–0x57; this 1010 is common to all serial EEPROMs), comes in 8-pin DIP/SOP/TSSOP/DFN and SOT-23-5 packages that fit existing footprints, with a 5ms (max) write cycle, ~1,000,000-cycle endurance, ~100-year retention and −40~+85°C industrial temperature. Overall it is a same-density alternative to AT24C / 24LC / M24C.
⚠️ The migration trap: page size (1K/2K differs most)
The easiest trap when swapping is the page size. A page write writes at most one page worth of bytes; writing past it rolls over within the page and overwrites old data — and the page size is not necessarily the same across vendors or densities. A confirmed difference: at 1K/2K density FMD FT24C01A/02A use a 16-byte page, while the classic Atmel AT24C01/AT24C02 use an 8-byte page (only at 4K and up do the two converge: 04/08/16 = 16B, 32/64 = 32B, 128/256 = 64B, 512 = 128B). So if your firmware was hard-coded to AT24C02’s 8-byte page, moving to FMD usually still runs (FMD’s 16B page is larger); but porting code written for FMD’s 16B back onto an 8B AT24C02 will roll over and overwrite. Before swapping, compare the bytes-per-page in both datasheets and confirm the firmware’s page boundary; also check the write-cycle time tWC (FMD specs 5ms max — if firmware uses a fixed delay it must be ≥5ms; ACK polling is safest) and whether the Vcc range covers your system voltage.
Address pins at higher density (A2/A1/A0 get repurposed)
A second easily-missed point is the address pins at higher density. Small capacities (≤2K) can use A0/A1/A2 to put several parts on one bus; but as capacity grows, some address bits get repurposed as the memory’s word-address — e.g. FT24C04A uses only A2/A1 (up to 4 on a bus), FT24C08A only A2 (up to 2), and FT24C16A uses none of A0–A2 (only one on a bus). And on a small SOT-23-5 package with few pins, A2/A1/A0 must be treated as fixed 0. If you put several EEPROMs on one I²C bus, when swapping confirm the new part’s address-pin behavior at that density matches the original design.
How to migrate (the steps)
The migration steps: 1) Match the capacity — map the AT24C / 24LC / M24C you use today to the same-number FT24C (24C02→FT24C02A … 24C512→FT24C512A; for 1Mbit use FT24C1024A, but the 1Mbit tier has more vendor-specific addressing/pinout, so verify case by case). 2) Check the page size (especially 1K/2K) and confirm the firmware’s page boundary. 3) Confirm tWC and the write method (switching to ACK polling is recommended). 4) Confirm Vcc and the package/address pins. List FMD FT24C as an AVL second source for your existing 24Cxx so you can switch quickly on a shortage or cost-down and spread single-vendor supply risk. JLink Technology is an authorized FMD (Fremont Micro Devices) distributor supplying FT24C (I²C), FT25C (SPI) and FT93C (Microwire) EEPROMs; send us the 24Cxx parts and quantities you use today and we will map the matching FT24C and reply with samples, datasheets and pricing.
Products mentioned
FT24C Series I²C EEPROM (2K ~ 256K bit)
The FT24C series are standard I²C serial EEPROMs spanning 2K to 256K bit (FT24C02 ~ FT24C256), compatible with industry-standard pinouts, with a wide 1.8V ~ 5.5V supply — widely used to store configuration parameters, calibration data, and serial numbers.
FT25C Series SPI EEPROM
The FT25C series are FMD SPI serial EEPROMs spanning 8Kb~64Kbit, with a wide 1.8~5.5V supply, up to 20MHz SPI clock, >1,000,000 write cycles, and 100-year retention, in SOIC8 / TSSOP8 / DIP8, compatible with industry-standard 25-series (25xxx) SPI EEPROMs. (Note: FMD's separate FT25H series is SPI NOR Flash, not EEPROM.)
FT93C Series Microwire (3-Wire) EEPROM
The FT93C series are FMD Microwire 3-wire serial EEPROMs spanning 1Kb/2Kb/4Kb (FT93C46/56/66), with selectable x8 or x16 organization, a 2.5~5.5V supply (1.8~5.5V on A grades), >1,000,000 write cycles, and 100-year data retention. In SOP8 / TSSOP8 / DIP8, compatible with industry-standard 93Cxx parts (ST M93Cxx, Microchip 93LCxx, AT93Cxx).
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