Microchip Technology 25AA040XT/ST

Overview

25AA040XT/ST from Microchip Technology Inc. is a 4 Kbit (512 × 8) SPI-compatible serial EEPROM with 1.8–5.5 V supply range, 1 MHz max clock frequency, and industrial temperature range (−40°C to +85°C). It features hardware write protection (WP), HOLD suspend functionality, and 16-byte page write capability. It is used in embedded system configuration storage, sensor calibration data retention, and firmware parameter backup where low-power nonvolatile memory is required.

For engineers reviewing the 25AA040XT/ST datasheet, 25AA040XT/ST pinout, 25AA040XT/ST application, or 25AA040XT/ST equivalent, this page delivers verified electrical specs, validated TSSOP-8 pin mapping, confirmed endurance (1M cycles), real-world use cases, and two technically documented alternative parts for design continuity.

Technical Context

The 25AA040XT/ST implements a standard SPI Mode 0,0 interface with separate SI (data in) and SO (data out) lines, CS-controlled selection, and SCK-synchronized transfers. Its internal architecture includes an 8-bit instruction register, automatic address incrementing during sequential reads, and a STATUS register with WIP, WEL, BP0/BP1 bits for write status and block protection control.

It supports four levels of array protection (none, upper 1/4, upper 1/2, or full), uses self-timed erase/write cycles (5 ms max), and integrates power-on write-disable circuitry, a write-enable latch, and high-impedance tri-state outputs on SO, SI, and SCK during HOLD or CS high. The device operates across 1.8–5.5 V and guarantees >200 years data retention.

Key Specifications

Pinout & Package

25AA040XT/ST is supplied in an 8-pin Thin Shrink Small Outline Package (TSSOP) with 0.65 mm pitch, 4.4 mm width, and lead-free matte tin finish. Pin numbering follows JEDEC-standard TSSOP orientation (pin 1 marked by beveled corner).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25AA040XT/ST, the 25AA040A-I/ST offers enhanced reliability and qualification without layout or firmware changes, while the AT25040B-SSHL-T provides higher speed and voltage flexibility at the cost of minor register-level compatibility work.

Availability

25AA040XT/ST is available at Aetrix Electronics and suitable for industrial sensor nodes, medical device calibration storage, and smart meter firmware patching requiring stable component supply, long-term obsolescence management, and traceable sourcing.

Supply support for 25AA040XT/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 25AA040XT/ST belongs to Microchip's 25XX040 family of SPI serial EEPROMs, designed specifically for low-voltage, low-power embedded systems requiring reliable, byte-addressable nonvolatile storage with hardware write protection.

FAQ

What is the maximum clock frequency supported by the 25AA040XT/ST?

The 25AA040XT/ST supports a maximum serial clock frequency of 1 MHz when operating across its full 1.8–5.5 V supply range. This limit is specified under industrial temperature conditions (−40°C to +85°C) and ensures reliable setup/hold timing for SI and SO signals. At 5.5 V, the device can sustain this rate; at lower voltages (e.g., 1.8 V), timing margins tighten but remain compliant per DS21204E AC characteristics table.

Does the 25AA040XT/ST support page write operations, and what is the page size?

Yes, the 25AA040XT/ST supports page write operations with a fixed page size of 16 bytes. This allows up to 16 contiguous bytes to be loaded into the write buffer before initiating an internal write cycle. Page boundaries align to addresses ending in 0x0F (e.g., 0x00–0x0F, 0x10–0x1F); crossing a boundary wraps the address pointer to the start of the same page, potentially overwriting earlier data in the buffer.

How does the HOLD pin function in the 25AA040XT/ST, and what are its timing requirements?

The HOLD pin in the 25AA040XT/ST suspends ongoing SPI communication without resetting the internal state. To activate HOLD, the pin must be pulled low while SCK is low; it must be returned high while SCK remains low to resume. During HOLD, SI, SCK, and SO enter high-impedance states, and all inputs except CS are ignored. Minimum HOLD setup/hold times are 100–200 ns depending on VCC.

What protection mechanisms prevent unintended writes to the 25AA040XT/ST memory array?

The 25AA040XT/ST employs multiple hardware and protocol-level protections: (1) a write-enable latch that must be set via WREN instruction before any write, (2) a dedicated WP pin that disables all writes when low, (3) power-on reset of the write-enable latch, and (4) automatic latch reset after each successful write or WRDI command. These layers ensure robust immunity to noise, brownouts, or software errors.

Is the 25AA040XT/ST pin-compatible with other variants like 25LC040XT/ST or 25C040XT/ST?

No - while the 25AA040XT/ST, 25LC040XT/ST, and 25C040XT/ST share identical TSSOP-8 pinout and mechanical footprint, they differ in VCC operating ranges (1.8–5.5 V vs. 2.5–5.5 V vs. 4.5–5.5 V) and maximum clock frequencies (1 MHz vs. 2 MHz vs. 3 MHz). Interchangeability requires verification of supply voltage, timing margins, and temperature range compatibility in the target application.