The DS1990A from Dallas Semiconductor (now Analog Devices via Maxim) is a Serial Number iButton - a 1-Wire identity device housed in a coin-shaped stainless-steel can. DS1990A-F5+ is the RoHS-compliant F5 MicroCan version, the flanged can that self-aligns into a clip holder. Touch it to a 1-Wire reader and it returns a guaranteed-unique number, making it a durable electronic "key" or tag.

Its content is a 64-bit lasered ROM: an 8-bit family code of 01h identifies it as a serial-number device, a 48-bit serial number is unique to every part ever made, and an 8-bit CRC lets the host verify the read. With over 281 trillion combinations the 48-bit field never repeats, so the DS1990A needs no programming - the identity is fixed at manufacture and cannot be altered.

Communication uses the 1-Wire protocol on a single data contact: the host issues a reset pulse, the iButton answers with a presence pulse, then ROM commands - Read ROM, Match ROM, Search ROM and Skip ROM - move the 64-bit value. Power is drawn parasitically from the data line (no battery, no VCC pin), and many iButtons can share one multidrop bus, each found by its unique number. The steel can shrugs off contact wear, making it suited to handheld and outdoor readers.

Note: Values are taken from the Dallas/Maxim DS1990A datasheet. Confirm every parameter against the latest official documentation before committing a design.

DS1990A-F5+ is supplied in the F5 MicroCan - a 16 mm stainless-steel coin can (17.35 mm overall, 16.25 mm contact face, 5.89 mm thick) with a flange ("F5") that self-aligns and snaps into a clip holder; "+" marks the RoHS-compliant lead-free finish. The same die is also offered in the F3 can (no flange). The lid forms the IO (1-Wire data) contact and the base forms GND - a spring reader touches both. The can face is laser-branded with the iButton logo, the 1-Wire mark and the part number. Package dimensions and contact assignment are shown below.

📄 Full specifications are detailed in the official Dallas/Maxim DS1990A datasheet.

The iButton has no conventional pins - just two can contacts and a fixed ROM:

• Lid - IO: 1-Wire data line (carries reset/presence and all ROM commands; parasitically powers the device).
• Base / flange - GND: Ground return, made through the can's metal rim.
• 64-bit ROM: 8-bit family code (01h) + 48-bit unique serial number + 8-bit CRC, laser-set and read-only.

The 64-bit ROM layout (CRC / serial number / family code) is shown below.

The parts below are related Dallas/Maxim 1-Wire serial-number devices in our catalog. They are not all drop-in replacements; verify the package, function and interface before substituting.

Selection Tips: Use the DS1990A-F5 when you need a rugged, contact-read token; the F3 is the flangeless can of the same part. The DS1992L adds writable memory in the same can. For a board-mounted silicon equivalent of the 64-bit ROM, the DS2401 (TO-92/SOIC) and DS2411 (SOT-223) solder down instead of being touched.

Dallas Semiconductor, now part of Analog Devices through Maxim Integrated, created the iButton family - 1-Wire devices sealed in a durable steel can. The DS1990A was the original Serial Number iButton, giving every part a guaranteed-unique 64-bit identity for electronic keys and tags.

The device is backed by full datasheet characterization and 1-Wire application notes on ROM commands, CRC checking and reader design - the details that determine reliable identification in the field.