Microchip Technology 25LC040AT-I/ST

Overview

25LC040AT-I/ST from Microchip Technology Inc. is a 4 Kbit SPI Serial EEPROM with 512 × 8-bit organization, 16-byte page write capability, and industrial temperature range (–40°C to +85°C). It operates from 2.5V to 5.5V, supports up to 10 MHz clock frequency, and features hardware write protection via WP pin and HOLD suspend functionality - used for firmware storage, calibration data retention, and configuration memory in microcontroller-based embedded systems.

For engineers reviewing the 25LC040AT-I/ST datasheet, 25LC040AT-I/ST pinout, 25LC040AT-I/ST application, or 25LC040AT-I/ST equivalent, this page delivers verified electrical specs, SPI timing constraints, package-specific pin mapping (TSSOP-8), block protection modes, and real-world use context for reliable BOM selection and layout integration.

Technical Context

The 25LC040AT-I/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 optional HOLD/WP control signals. Its internal architecture includes a 512-byte EEPROM array, page latches, status register (WIP/WEL/BP0/BP1), and high-voltage generator for erase/write cycles.

It supports byte and page write operations with self-timed internal write cycles (≤5 ms), sequential read with automatic address increment, and configurable block protection (none/1/4/1/2/all array). The HOLD pin suspends ongoing SPI transfers without resetting state, enabling interrupt servicing in resource-constrained hosts.

Key Specifications

Pinout & Package

25LC040AT-I/ST is packaged in an 8-lead TSSOP (Thin Shrink Small Outline Package) with 0.65 mm pitch, marked "5L4AT" per Microchip's marking convention. Pin 1 is identified by laser mark; exposed pad is not present in this variant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25LC040AT-I/ST, 25AA040AT-I/ST adds 1.8V operation at the cost of slightly higher standby current, while AT25040B-SSHL-T offers identical functionality with broader automotive qualification - enabling design reuse across industrial and automotive platforms without layout changes.

Availability

25LC040AT-I/ST is available at Aetrix Electronics and suitable for industrial automation controllers, automotive body electronics, medical handheld diagnostics, and smart metering systems requiring stable component supply, long-term obsolescence management, and RoHS-compliant sourcing.

Supply support for 25LC040AT-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 infrastructure.

The 25LC040A family was designed specifically for cost-sensitive, space-constrained embedded systems needing reliable, low-power serial EEPROM with robust SPI interoperability and hardware-based data protection.

FAQ

What is the maximum clock frequency supported by the 25LC040AT-I/ST?

The 25LC040AT-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, and at 1.8V ≤ VCC < 2.5V it drops to 3 MHz. These limits are defined in Table 1-2 of the DS21827H datasheet and ensure reliable setup/hold timing across voltage and temperature ranges. The 25LC040AT-I/ST does not support 10 MHz operation below 4.5V.

Does the 25LC040AT-I/ST require external pull-up resistors on SI, SO, or HOLD pins?

No external pull-ups are required on SI, SO, or HOLD for normal operation. SI is a CMOS input with internal bias not specified; SO is actively driven or tri-stated (no pull-up needed); HOLD is CMOS input with no internal pull-up. However, weak external pull-ups (e.g., 10 kΩ) on HOLD and WP may improve noise immunity in electrically noisy environments. The 25LC040AT-I/ST datasheet does not mandate them, but system-level EMC testing may justify their use.

How does the page write function work in the 25LC040AT-I/ST?

The 25LC040AT-I/ST supports page writes of up to 16 bytes within a single 16-byte physical page boundary (e.g., addresses 0x00–0x0F). After issuing WREN and WRITE instructions with a starting address, up to 16 bytes can be clocked in sequentially. If more than 16 bytes are sent or the address crosses a page boundary, data wraps to the start of the same page - overwriting earlier bytes. This behavior is documented in Section 2.3 and Figure 2-3 of the DS21827H datasheet for the 25LC040AT-I/ST.

What happens to the write enable latch during power-up of the 25LC040AT-I/ST?

On power-up, the write enable latch in the 25LC040AT-I/ST is automatically reset (WEL = 0), disabling all write operations until a WREN instruction is successfully issued. This is confirmed in Section 2.8 (Power-On State) and Table 2-4 (Write-Protect Functionality Matrix) of the DS21827H datasheet. The 25LC040AT-I/ST remains in standby mode with SO in high-impedance until CS is asserted, ensuring no spurious writes occur during voltage ramp-up.

Can the 25LC040AT-I/ST be used with a 1.8V microcontroller?

No, the 25LC040AT-I/ST has a minimum VCC of 2.5V and is not rated for 1.8V operation. Attempting to power it at 1.8V will result in undefined behavior, failed writes, or communication errors. For 1.8V systems, the pin-compatible 25AA040AT-I/ST (1.8–5.5V range) is the correct alternative. Both share identical instruction set, timing, and TSSOP-8 packaging, but the 25LC040AT-I/ST specification explicitly excludes 1.8V use per Device Selection Table on DS21827H-page 1.