Microchip Technology 25LC040AXT-E/ST

Overview

25LC040AXT-E/ST from Microchip Technology is a 4 Kbit SPI Serial EEPROM with 512 × 8-bit organization, 16-byte page write capability, and industrial-temperature operation (–40°C to +85°C). It supports up to 10 MHz clock frequency at 4.5–5.5 V, features hardware write protection via WP pin and STATUS register block protection, and is used for configuration storage in microcontroller-based embedded systems.

For engineers reviewing the 25LC040AXT-E/ST datasheet, 25LC040AXT-E/ST pinout, 25LC040AXT-E/ST application, or 25LC040AXT-E/ST equivalent, key selection criteria include SPI interface timing compliance, VCC range (2.5–5.5 V), page write boundary handling, HOLD functionality for interrupt-safe bus arbitration, and automotive-grade temperature support in the E-temp variant.

Technical Context

The 25LC040AXT-E/ST implements a standard SPI Mode 0,0 / 1,1 interface with separate SI (data in) and SO (data out) lines, CS-controlled selection, and HOLD pin for pausing ongoing transfers without sequence restart. Its internal architecture includes an 8-bit instruction register, page latches, and high-voltage generator for EEPROM programming.

Write operations require explicit WREN instruction followed by CS high to latch enable state; writes are self-timed (≤5 ms), and status polling via RDSR (WIP bit) is required to confirm completion. Block protection (BP0/BP1) enables selective write-disable of 0%, 25%, 50%, or 100% of the 512-byte array.

Key Specifications

Pinout & Package

25LC040AXT-E/ST is packaged in an 8-lead TSSOP (ST package code), 3.0 mm × 4.4 mm body, 0.65 mm pitch, with pin 1 marked by laser indentation. Pin functions align with standard SPI EEPROM topology and support board-level write protection and bus hold functionality.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25LC040AXT-E/ST, the 25AA040AT-I/ST extends voltage flexibility downward but sacrifices automotive qualification, while the AT25040B-SSHL-T reduces feature set (no HOLD, no BP bits) to lower unit cost - trade-offs center on environmental robustness versus functional completeness.

Availability

25LC040AXT-E/ST is available at Aetrix Electronics and suitable for industrial automation, automotive electronics, and medical instrumentation requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for 25LC040AXT-E/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 components, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25LC040A family targets cost-sensitive, space-constrained embedded systems needing reliable nonvolatile storage - optimized for seamless integration with PIC® and dsPIC® microcontrollers via native SPI.

FAQ

What is the maximum clock frequency supported by the 25LC040AXT-E/ST, and how does it vary with supply voltage?

The 25LC040AXT-E/ST supports up to 10 MHz clock frequency when VCC is between 4.5 V and 5.5 V. At 2.5 V ≤ VCC < 4.5 V, the maximum clock drops to 5 MHz, and no specification is provided below 2.5 V. These limits are defined in Table 1-2 of the DS21827H datasheet and must be observed to ensure reliable SPI communication - exceeding them risks data corruption or failed writes. The 25LC040AXT-E/ST does not operate at 10 MHz across its full 2.5–5.5 V range.

How does the HOLD pin function during an active SPI transfer in the 25LC040AXT-E/ST?

The HOLD pin in the 25LC040AXT-E/ST suspends an ongoing SPI transfer without resetting the internal state: when pulled low (while SCK is low), SI, SO, and SCK enter high-impedance, and the device pauses exactly where it left off. Resuming requires bringing HOLD high while SCK remains low. This allows the host MCU to service time-critical interrupts and resume the exact same byte position - essential for deterministic real-time systems. The 25LC040AXT-E/ST HOLD behavior is fully specified in Figure 1-1 and Section 2.1.

Can the 25LC040AXT-E/ST perform page writes across memory boundaries, and what happens if it does?

No - the 25LC040AXT-E/ST cannot safely perform page writes across 16-byte physical page boundaries. If a page write command attempts to cross a boundary (e.g., writing 16 bytes starting at address 0x0F), the address counter wraps to the start of the same page (0x00), overwriting previously written data in that page. This behavior is explicitly documented in Section 2.3 and Note on DS21827H-page 6. Firmware must validate starting addresses and byte counts to stay within page limits before issuing WRITE commands to the 25LC040AXT-E/ST.

What write protection mechanisms are implemented in the 25LC040AXT-E/ST, and how do they interact?

The 25LC040AXT-E/ST implements three layered protections: (1) WP pin (hardware, overrides all), (2) WEL bit (software-latched, reset on power-up/WREN/WRDI), and (3) BP0/BP1 bits (nonvolatile, define protected memory blocks). Per Table 2-4, WP low disables all writes regardless of WEL or BP state. When WP is high, WEL must be set to enable writes, and BP bits determine which address ranges remain write-protected even with WEL=1. All mechanisms are verified in the DS21827H datasheet and apply identically to the 25LC040AXT-E/ST.

Is the 25LC040AXT-E/ST pin-compatible with other members of the 25XX040A family, and which packages share identical pinouts?

Yes - the 25LC040AXT-E/ST (TSSOP, ST package) shares identical pinout and function mapping with all 8-lead variants in the 25XX040A family, including PDIP (P), SOIC (SN), MSOP (MS), DFN (MN), and TDFN (MC) packages, as confirmed in Table 3-1 and Package Types diagrams on DS21827H-pages 1–2. Pin 1 (CS) through Pin 8 (VCC) maintain consistent signal assignment across these packages. However, the 6-lead SOT-23 variant (OT) has a different pin count and layout and is not compatible with the 25LC040AXT-E/ST.