Microchip Technology 25AA640XT-I/ST

Overview

25AA640XT-I/ST from Microchip Technology Inc. is a 64 Kbit SPI Serial EEPROM with 8192 × 8-bit organization, 1.8–5.5 V supply range, and industrial temperature rating (−40°C to +85°C). It features 32-byte page write capability, 5 ms max internal write cycle time, and hardware write protection via WP pin and STATUS register. It is used in embedded systems for nonvolatile parameter storage, calibration data retention, and firmware configuration in space-constrained industrial controllers.

For engineers reviewing the 25AA640XT-I/ST datasheet, 25AA640XT-I/ST pinout, 25AA640XT-I/ST application, or 25AA640XT-I/ST equivalent, this page delivers verified electrical specs, TSSOP-8 pin mapping, real-world use cases, and two validated alternative parts - all aligned to DS21223H revision H and Microchip's official packaging & functional documentation.

Technical Context

The 25AA640XT-I/ST implements a standard SPI Mode 0,0 or Mode 1,1 interface with separate SI (data in) and SO (data out) lines, CS-controlled selection, and HOLD-enabled transaction suspension. Its internal architecture includes an 8-bit instruction register, auto-incrementing address pointer for sequential reads, and a nonvolatile STATUS register with WIP, WEL, BP0/BP1, and WPEN bits.

Write operations require explicit WREN instruction followed by WRITE command; page writes are limited to 32 bytes within the same 32-byte boundary (e.g., 0x0000–0x001F). Block protection supports four configurations: no protection, upper 1/4 (0x1800–0x1FFF), upper 1/2 (0x1000–0x1FFF), or full array (0x0000–0x1FFF), controlled via BP0/BP1 bits.

Key Specifications

Pinout & Package

25AA640XT-I/ST is housed in an 8-pin Plastic Thin Shrink Small Outline Package (TSSOP) with 0.65 mm lead pitch and 4.4 mm body width, optimized for high-density PCB layouts and automated SMT assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM applications.

Compared with 25AA640XT-I/ST, the 25AA640A-I/ST offers drop-in replacement assurance and extended lifecycle support, while the AT25DF041A-SSH-T provides higher density at the cost of command incompatibility and loss of HOLD functionality - making it unsuitable for interrupt-driven real-time parameter updates.

Availability

25AA640XT-I/ST is available at Aetrix Electronics and suitable for industrial PLCs, medical diagnostics equipment, smart energy meters, and automotive body control modules requiring stable component supply across extended production lifecycles.

Supply support for 25AA640XT-I/ST includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Microchip Technology Inc. is a leading provider of microcontroller, analog, and Flash-IP solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25AA640XT-I/ST belongs to Microchip's legacy SPI Serial EEPROM product line, engineered for low-voltage, low-power, and high-reliability nonvolatile data storage in resource-constrained embedded systems.

FAQ

What is the maximum clock frequency supported by the 25AA640XT-I/ST?

The 25AA640XT-I/ST supports up to 1 MHz maximum SPI clock frequency across its full 1.8–5.5 V supply range and −40°C to +85°C industrial temperature range. This limit ensures reliable setup/hold timing margins per DS21223H Table 1-2, especially under worst-case voltage and temperature conditions. Exceeding 1 MHz may cause read/write failures due to violated TCSS, TCSH, or TSU timing requirements.

Does the 25AA640XT-I/ST support page write operations, and what is the page size?

Yes, the 25AA640XT-I/ST supports page write operations with a fixed page size of 32 bytes. Writes must remain within the same page boundary (e.g., addresses 0x0000–0x001F); crossing page boundaries automatically wraps the internal address pointer and overwrites earlier bytes in the page. This behavior is defined in Section 3.3 of DS21223H and applies identically to 25AA640XT-I/ST.

How does the HOLD pin function during an active SPI transaction on the 25AA640XT-I/ST?

The HOLD pin on the 25AA640XT-I/ST suspends ongoing SPI communication without resetting the internal state. When pulled low while SCK is low, SI/SO/SCK enter high-impedance states and all inputs except CS are ignored. To resume, HOLD must be raised while SCK remains low. This enables the host MCU to service urgent interrupts (e.g., timer expiry or CAN message arrival) and continue the exact same transaction afterward - a capability confirmed in Section 2.6 and Figure 1-1 of DS21223H.

What write protection mechanisms are implemented in the 25AA640XT-I/ST?

The 25AA640XT-I/ST implements three layered write protections: (1) software-controlled WREN/WRDI instruction gating, (2) nonvolatile BP0/BP1 bits for 0%/25%/50%/100% array block protection, and (3) hardware WP pin + WPEN bit combination that disables STATUS register writes when both are active. These mechanisms are fully documented in Sections 3.5–3.6 and Table 3-3 of DS21223H and apply directly to the 25AA640XT-I/ST variant.

Is the 25AA640XT-I/ST pin-compatible with other packages in the 25XX640 family?

No - the "XT" suffix denotes the TSSOP package with alternate pinout (CS=3, SO=4, WP=5, VSS=6, SI=7, SCK=8, HOLD=1, VCC=2), which differs from standard SOIC/PDIP pin assignments. While electrically identical, PCB layout must match the TSSOP-8 footprint and pin mapping shown in Figure 2-1 and Table 2-1 of DS21223H. Substituting 25AA640XT-I/ST for SN- or P-packaged variants requires board redesign.