Microchip Technology 25LC640AX-I/ST

Overview

25LC640AX-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 (at VCC ≥ 4.5V), supports hardware write protection via WP pin and STATUS register, and delivers 1 million erase/write cycles with >200-year data retention. It is used in microcontroller-based systems for nonvolatile parameter storage, calibration data logging, and firmware configuration.

For engineers reviewing the 25LC640AX-I/ST datasheet, 25LC640AX-I/ST pinout, 25LC640AX-I/ST application, or 25LC640AX-I/ST equivalent, key selection criteria include SPI interface compatibility, 2.5V–5.5V supply range, page-write timing (≤5 ms), HOLD functionality for interrupt-safe operation, and block-level write protection granularity (none/¼/½/all array).

Technical Context

The 25LC640AX-I/ST implements a standard SPI Mode 0,0/Motorola-compatible serial interface with separate SI (data in) and SO (data out) lines, requiring only CS, SCK, SI, SO, WP, HOLD, VCC, and VSS. Its internal architecture includes a 32-byte page latch, status register with WIP/WEL/BP0/BP1/WPEN bits, and high-voltage generator for EEPROM programming.

It supports sequential read with automatic address increment, byte/page write with CS-high-triggered internal write cycle (TWC ≤ 5 ms), and HOLD pin assertion to pause ongoing transfers without resetting the command sequence - enabling deterministic host interrupt handling while preserving bus state.

Key Specifications

Pinout & Package

25LC640AX-I/ST is packaged in an 8-lead SOIC (SN) with 3.90 mm body width, RoHS-compliant, and marked "25LC640A" on top. Pin 1 is located at the top-left corner with notch or dot indicator.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25AA640AT-I/ST, the 25LC640AX-I/ST trades 1.8V operation for enhanced noise immunity above 2.5V; versus AT25DF641-AU, it provides true EEPROM behavior-no erase-before-write, deterministic 5 ms writes, and dedicated hardware protection-making it irreplaceable for mission-critical configuration storage.

Availability

25LC640AX-I/ST is available at Aetrix Electronics and suitable for industrial sensor nodes, automotive body control modules, and medical infusion pumps requiring stable component supply, long-lifecycle support, and AEC-Q100-qualified reliability.

Supply support for 25LC640AX-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 family is designed for cost-sensitive, space-constrained embedded systems needing reliable, low-power serial nonvolatile storage - optimized for integration with PIC® and dsPIC® microcontrollers and compliant with industrial and automotive environmental standards.

FAQ

What is the maximum clock frequency supported by the 25LC640AX-I/ST?

The 25LC640AX-I/ST supports up to 10 MHz clock frequency when VCC is 4.5V to 5.5V. At 2.5V ≤ VCC < 4.5V, the maximum is 5 MHz; at 1.8V ≤ VCC < 2.5V, it drops to 3 MHz. These limits ensure setup/hold timing compliance across voltage and temperature ranges. The 25LC640AX-I/ST datasheet specifies AC characteristics for each VCC band, and all timing parameters (e.g., TCSS, TSU) scale accordingly.

Does the 25LC640AX-I/ST require external pull-up resistors on its SPI lines?

No, the 25LC640AX-I/ST does not require external pull-ups on SI, SO, or SCK - these pins are actively driven. However, CS and WP should be pulled high via 10 kΩ resistors in most designs to ensure defined states during reset or floating conditions. HOLD also benefits from a weak pull-up (100 kΩ) to prevent spurious pauses. The 25LC640AX-I/ST internal input leakage is ±1 µA, making external biasing straightforward and low-power.

How does the HOLD function behave during an active write cycle in the 25LC640AX-I/ST?

The HOLD pin has no effect on an ongoing internal write cycle (TWC) in the 25LC640AX-I/ST. Once CS rises after a valid write sequence, the 5 ms internal write begins and cannot be interrupted or paused by HOLD. HOLD only suspends serial communication (read/write instructions, address, data) - it does not halt EEPROM cell programming. The 25LC640AX-I/ST STATUS register's WIP bit remains set until TWC completes, regardless of HOLD state.

Can the 25LC640AX-I/ST be used in automotive applications?

Yes, the 25LC640AX-I/ST is AEC-Q100 qualified for automotive applications and rated for the Industrial temperature range (–40°C to +85°C), which covers most under-hood and cabin environments. Its 2.5V–5.5V supply range aligns with automotive 5V and 3.3V domains, and features like hardware write protection (WP pin + STATUS register), >4 kV ESD, and 1M endurance meet automotive reliability requirements. The 25LC640AX-I/ST is commonly deployed in body control modules and infotainment subsystems.

What happens to the write enable latch after a successful write operation in the 25LC640AX-I/ST?

After a successful WRITE, WRSR, or WRDI instruction, the write enable latch (WEL bit) in the 25LC640AX-I/ST is automatically reset to '0'. This means the device immediately disables further writes until WREN is issued again. Power-up, WRSR execution, and WRDI all clear WEL - enforcing strict write gating. The 25LC640AX-I/ST STATUS register reflects this change: WEL=0 indicates write-disabled state, preventing accidental overwrites even if CS remains asserted.