55 ns parallel Flash in a 32-PLCC footprint
The Microchip SST39LF040-55-4C-NHE is a 4Mbit parallel Flash memory from the SST39 MPF™ series, organized as 512K x 8 bits. The 20 µs word/page write cycle time suits firmware-update routines where the host processor manages the erase-and-write sequence. This is a commercial-temperature device (0°C to 70°C), intended for indoor, non-condensing environments like office equipment, industrial controllers, or test instrumentation.
55 ns access — timing margin on the bus
The 55 ns access time is the spec that determines whether this part can keep up with your memory controller without wait states. At a 20 MHz bus clock (50 ns period), a 55 ns access leaves negative margin for a single-cycle read — you will need at least one wait state inserted. For a 16 MHz bus (62.5 ns period), the 55 ns access fits with about 7.5 ns of setup margin, which is tight but workable if the PCB trace delay is under 2 ns. Budget the access time against your controller's read-cycle timing, not just the clock frequency.
The supply range of 3V to 3.6V means this part operates on a 3.3V rail, with no 5V tolerance on the I/O pins. If your system uses a 5V bus, you will need level translation or a different Flash variant. The 3.3V-only requirement is common for low-power embedded systems, but it rules out direct connection to legacy 5V logic families.