Microchip Technology 25LC640A-I/ST

Overview

25LC640A-I/ST from Microchip Technology Inc. is a 64-Kbit SPI Serial EEPROM with 8192 × 8-bit organization, 32-byte page size, and industrial temperature range (–40°C to +85°C). It operates at up to 10 MHz clock frequency with 5 mA read/write current at 5.5 V and supports hardware write protection via WP pin and STATUS register. It is used in microcontroller-based systems for nonvolatile parameter storage, calibration data retention, and firmware configuration.

For engineers reviewing the 25LC640A-I/ST datasheet, 25LC640A-I/ST pinout, 25LC640A-I/ST application, or 25LC640A-I/ST equivalent, key selection criteria include SPI timing compliance at 2.5–5.5 V supply, page-write boundary handling, HOLD functionality for interrupt-safe bus arbitration, and block protection granularity (none/1/4/1/2/all).

Technical Context

The 25LC640A-I/ST implements a standard SPI Mode 0,0/Modes 1,1 interface with separate SI (data-in) and SO (data-out) lines, requiring CS, SCK, and optional HOLD/WP control. Its internal architecture includes a 32-byte page latch, status register with WIP/WEL/BP0/BP1 bits, and high-voltage generator for EEPROM programming.

Write operations require explicit WREN instruction before WRITE or WRSR commands; CS rising edge initiates self-timed internal write cycle (≤5 ms). HOLD suspends ongoing serial transfers without resetting address pointers, enabling host CPU to service higher-priority interrupts while preserving transaction state.

Key Specifications

Pinout & Package

25LC640A-I/ST is packaged in an 8-lead SOIC (SN) with 3.90 mm body width, RoHS-compliant matte tin finish, and standard JEDEC MS-012AC footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT25DF041A-SSH-T and 25AA640A-I/ST, the 25LC640A-I/ST offers optimal balance of industrial temperature support, proven 1M-cycle endurance, and minimal firmware integration effort - making it preferred for cost-sensitive, medium-density configuration storage where quad-SPI or sub-2.5 V operation is unnecessary.

Availability

25LC640A-I/ST is available at Aetrix Electronics and suitable for industrial sensor nodes, automotive body control modules, medical diagnostic equipment, and smart energy meters requiring stable component supply and long-term lifecycle assurance.

Supply support for 25LC640A-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 microcontrollers, analog devices, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25LC640A belongs to Microchip's serial EEPROM product line, engineered for robust, low-power nonvolatile data storage in resource-constrained embedded systems across industrial, automotive, and medical applications.

FAQ

What is the maximum clock frequency supported by the 25LC640A-I/ST?

The 25LC640A-I/ST supports a maximum clock frequency of 10 MHz when VCC is between 4.5 V and 5.5 V. At 2.5 V ≤ VCC < 4.5 V, the maximum clock is 5 MHz; below 2.5 V, it drops to 3 MHz. These limits ensure reliable setup/hold timing for SI and SO signals across voltage and temperature ranges specified in the AC characteristics table.

Does the 25LC640A-I/ST require external pull-up resistors on its SPI lines?

The 25LC640A-I/ST does not require external pull-ups on SI, SCK, or CS - these inputs have CMOS-compatible thresholds and function correctly with standard MCU GPIO outputs. However, SO is open-drain capable only when configured for shared-bus operation; in point-to-point configurations, no pull-up is needed as SO actively drives high/low. WP and HOLD should be pulled high externally if unused.

How does the HOLD pin function during an active SPI transaction in the 25LC640A-I/ST?

During an active SPI transaction, asserting HOLD low (while SCK is low) places the 25LC640A-I/ST into hold mode: SI, SCK, and SO enter high-impedance states, and all input transitions except CS are ignored. The internal address pointer and instruction state are preserved. To resume, HOLD must be raised while SCK remains low - resuming exactly where the transaction paused, without retransmission.

Can the 25LC640A-I/ST be used in automotive applications?

Yes - the 25LC640A-I/ST is AEC-Q100 qualified for automotive applications and rated for extended temperature operation (–40°C to +125°C). Its 1M write endurance, >200-year data retention, and hardware write protection make it suitable for body control modules, infotainment configuration storage, and ADAS sensor calibration data retention.

What happens if a page write crosses a 32-byte boundary in the 25LC640A-I/ST?

If a page write command attempts to cross a 32-byte boundary (e.g., writing bytes starting at address 0x001F), the 25LC640A-I/ST wraps the data to the start of the same page (e.g., overwriting 0x0000–0x0000 instead of writing to 0x0020). This causes unintended data corruption. Application firmware must enforce page-aligned writes or split multi-page transfers manually before issuing WRITE commands.