Microchip Technology 25AA040A-I/ST

Overview

25AA040A-I/ST from Microchip Technology Inc. is a 4 Kbit SPI Serial EEPROM with 512 × 8-bit organization, 1.8–5.5 V supply range, and industrial temperature rating (–40°C to +85°C). It supports up to 10 MHz clock frequency, 16-byte page write mode, and hardware write protection via WP pin. It is used in embedded systems for storing calibration data, configuration settings, and firmware parameters.

For engineers reviewing the 25AA040A-I/ST datasheet, 25AA040A-I/ST pinout, 25AA040A-I/ST application, or 25AA040A-I/ST equivalent, this page provides verified electrical specs, SPI timing constraints, package-specific pin mapping (TSSOP-8), block protection behavior, and real-world use cases in microcontroller-based control systems.

Technical Context

The 25AA040A-I/ST implements a standard SPI Mode 0,0 or Mode 1,1 interface with separate SI/SO lines and active-low CS. It uses an internal 9-bit address space (A8–A0) to access its 512-byte array, with automatic address roll-over during sequential reads. The HOLD pin enables mid-transaction suspension without bus reinitialization.

Its STATUS register exposes WIP (Write-In-Process), WEL (Write Enable Latch), and BP0/BP1 bits for nonvolatile block protection-configurable to protect none, upper 1/4, upper 1/2, or all memory. Write cycles are self-timed (≤5 ms), and the device resets WEL on power-up, WRDI, WRSR, WRITE completion, or WP low assertion.

Key Specifications

Pinout & Package

25AA040A-I/ST is packaged in an 8-lead TSSOP (Thin Shrink Small Outline Package) with 0.65 mm pitch, marked "ST" in Microchip's package code table. 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 25LC040A-I/ST, the 25AA040A-I/ST enables 1.8 V operation and offers identical industrial-temp reliability, while AT25040B-SSHL-T sacrifices HOLD/WP functionality and doubles standby current - making 25AA040A-I/ST optimal for low-voltage, interrupt-driven, and write-critical designs.

Availability

25AA040A-I/ST is available at Aetrix Electronics and suitable for industrial automation controllers, medical diagnostic instruments, and automotive body electronics requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for 25AA040A-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 25AA040A belongs to Microchip's serial EEPROM product line, designed specifically for reliable, low-power, SPI-based nonvolatile storage in cost-sensitive and space-constrained embedded systems.

FAQ

What is the maximum clock frequency supported by the 25AA040A-I/ST?

The 25AA040A-I/ST supports up to 10 MHz clock frequency when VCC is 4.5 V to 5.5 V. At 2.5 V ≤ VCC < 4.5 V, max clock drops to 5 MHz; at 1.8 V ≤ VCC < 2.5 V, it is limited to 3 MHz. These limits ensure setup/hold timing compliance across voltage and temperature ranges per DS21827H Table 1-2.

Does the 25AA040A-I/ST require external pull-up resistors on its SPI lines?

No, the 25AA040A-I/ST does not require external pull-up resistors on SI, SO, SCK, or CS. Its inputs meet VIH/VIL thresholds across 1.8–5.5 V, and SO is actively driven or tri-stated - pull-ups would interfere with proper SPI signaling and are omitted in all reference schematics for this device.

How does the HOLD pin function during an ongoing SPI read operation?

When HOLD is pulled low during an SPI read, the 25AA040A-I/ST immediately places SO in high-impedance and ignores further SCK transitions, freezing the internal address counter. Upon returning HOLD high (while SCK is low), the device resumes reading from the exact byte where it paused - preserving data coherency without retransmission.

Can the 25AA040A-I/ST be used in a 5 V system with a 3.3 V microcontroller?

Yes - the 25AA040A-I/ST is specified for 1.8–5.5 V operation and has VIH = 0.7×VCC, so at VCC = 5 V, VIH = 3.5 V. A 3.3 V MCU's logic-high output (~3.3 V) falls below this threshold. Therefore, level translation (e.g., TXB0104) or VCC = 3.3 V operation is required for reliable communication.

What happens if a page write crosses a 16-byte boundary on the 25AA040A-I/ST?

If a page write command attempts to write across a 16-byte boundary (e.g., starting at address 0x0F and writing 16 bytes), the 25AA040A-I/ST wraps the excess bytes to the start of the same page (0x00–0x0E), overwriting prior data. This behavior is documented in DS21827H Section 2.3 and requires firmware to enforce page alignment before issuing WRITE commands.