Microchip Technology 25LC040AT-E/ST

Overview

25LC040AT-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 block protection (BP0/BP1), and delivers 1 million erase/write cycles with >200-year data retention - used in embedded system configuration storage and firmware parameter logging.

For engineers reviewing the 25LC040AT-E/ST datasheet, 25LC040AT-E/ST pinout, 25LC040AT-E/ST application, or 25LC040AT-E/ST equivalent, key selection criteria include SPI interface compatibility, 16-byte page boundary handling, HOLD pin support for interrupt-safe bus suspension, VCC range (2.5–5.5 V), and TSSOP-8 package footprint constraints.

Technical Context

The 25LC040AT-E/ST implements a standard SPI Mode 0,0/Master-Slave interface with separate SI (data in) and SO (data out) lines, requiring CS, SCK, and HOLD control. Its internal architecture includes an 8-bit instruction register, status register (WIP/WEL/BP0/BP1), and page latches enabling atomic 16-byte writes within fixed 0x00–0x0F boundaries per page.

Write operations require explicit WREN instruction followed by CS high-to-low transition to initiate self-timed internal write cycle (≤5 ms); read operations support sequential addressing with automatic address roll-over at 0x1FF. The HOLD pin suspends ongoing transfers while preserving internal state, allowing host MCU to service higher-priority interrupts without reinitializing the SPI sequence.

Key Specifications

Pinout & Package

25LC040AT-E/ST is housed in an 8-lead TSSOP package (ST suffix), 3.0 mm × 4.4 mm body, 0.65 mm pitch, with exposed pad optional for thermal relief. Pin 1 marked by laser dot; pin 1 location confirmed per Microchip DS21827H-page 30 diagram.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25AA040AT-I/ST, the 25LC040AT-E/ST trades 1.8 V operation for guaranteed automotive-qualified temperature range and tighter VCC min spec; versus AT25040B-SSHL-T, it adds HOLD and precise block protection at the cost of 10 MHz vs. 20 MHz max clock - making it optimal for robust industrial control and automotive body electronics.

Availability

25LC040AT-E/ST is available at Aetrix Electronics and suitable for industrial PLCs, automotive body control modules, medical diagnostic calibration storage, and smart energy meter firmware parameter retention requiring stable component supply across multi-year production cycles.

Supply support for 25LC040AT-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 microcontroller, analog, FPGA, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25LC040A family is designed for reliable, low-power nonvolatile data storage in resource-constrained embedded systems, emphasizing SPI simplicity, write robustness, and long-term data integrity in harsh environments.

FAQ

What is the maximum clock frequency supported by the 25LC040AT-E/ST, and how does it vary with supply voltage?

The 25LC040AT-E/ST supports up to 10 MHz at VCC = 4.5–5.5 V, 5 MHz at 2.5–4.5 V, and no specified operation below 2.5 V. These limits are defined in Table 1-2 of DS21827H and ensure reliable setup/hold timing across voltage and temperature ranges. Exceeding these frequencies risks read/write corruption due to violated AC timing parameters like TCSS, Tsu, and THD.

How does the HOLD pin function during an active SPI transaction in the 25LC040AT-E/ST?

The HOLD pin in the 25LC040AT-E/ST suspends ongoing SPI communication when pulled low while SCK is low, placing SI, SO, and SCK in high-impedance state without resetting the internal address pointer or instruction state. To resume, HOLD must be raised while SCK remains low. This allows the host MCU to service time-critical interrupts and return to the exact point in the SPI sequence - a feature confirmed in Section 2.8 and Figure 1-1 of DS21827H.

What are the page write boundaries for the 25LC040AT-E/ST, and why is alignment critical?

The 25LC040AT-E/ST has fixed 16-byte physical pages starting at addresses 0x00, 0x10, 0x20…0xF0. Page writes crossing boundaries (e.g., writing 16 bytes starting at 0x0F) wrap around to the page start (0x00), overwriting prior data. This behavior is explicitly documented in Section 2.3 and Note under Figure 2-3 of DS21827H, making firmware-level address alignment mandatory for data integrity.

Does the 25LC040AT-E/ST support hardware write protection independent of software controls?

Yes - the 25LC040AT-E/ST includes a dedicated WP pin (Pin 3) that, when held low, disables all writes to both memory array and STATUS register regardless of WEL bit state or WREN instruction. This hardware lock operates independently of software controls and is validated in Table 2-4 and Section 3.3 of DS21827H, providing fail-safe protection against firmware bugs or voltage glitches.

What is the endurance specification for the 25LC040AT-E/ST, and under what conditions is it guaranteed?

The 25LC040AT-E/ST guarantees 1,000,000 erase/write cycles at 25°C and VCC = 5.5 V, as stated in Table 1-3 (Param. 21) of DS21827H. Endurance decreases at elevated temperatures and lower VCC; Microchip's Total Endurance™ Model (available at microchip.com) provides application-specific estimates based on actual operating conditions - not extrapolated or assumed.