"Tri" this flash-memory form factor

-- EDN, 12/7/2000

Sandisk is gradually switching from the EEPROM-based NOR flash memory that it's used for many years to a NAND-based technology that it's co-developing with Toshiba (www.toshiba.com). Even at the same densities, NOR and NAND flash memories differ from each other in numerous aspects, including erase-block size, erase and write speeds, random and sequential read performance, package, and pinout. Vendors can sometimes hide these differences, though, by putting the memory array behind a media controller supporting an industry-standard interface, such as PCMCIA, CompactFlash, or MultiMedia Card (see "Memory cards: designing with a full deck," EDN, May 25, 2000, pg 69). With a good memory-controller design, you may even be unable to tell that the manufacturer is using inexpensive but often low-performance multilevel-cell technology.

Multi-memory-sourcing diversity is all well and good with removable media, but what if all you need is resident storage, or you require a mix of fixed and replaceable or upgradable memory? Sandisk has used a trick it first employed with its ATA-interface chip set and borrowed the MultiMediaCard protocol it also pioneered to come up with the TriFlash product line (Picture). Initially available in $35 (1000), 128-Mbit; $60, 256- Mbit; and $110, 512-Mbit densities, TriFlash devices bundle flash memory and a media controller inside a common-footprint, thin-fine-pitch BGA package measuring 17×12 mm and 1.2 mm thick. You can chain together as many as 32 TriFlash and MultiMediaCard devices in any proportion along the same three-pin SPI (serial-peripheral-interface) bus. Sandisk schedules production for the first half of 2001.

Sandisk, 1-408-542-0500, www.sandisk.com.

—by Brian Dipert