Microchip Technology 25AA256-E/ST

Overview

25AA256-E/ST from Microchip Technology Inc. is a 256 Kbit (32,768 × 8) SPI-compatible serial EEPROM with 1.8–5.5 V supply range, 64-byte page write capability, and automotive-grade temperature support (–40°C to +125°C). It features hardware write protection via WP pin and STATUS register, self-timed 5 ms max write cycles, and 1 million endurance cycles - deployed in engine control units, industrial sensor nodes, and medical device configuration storage.

For engineers reviewing the 25AA256-E/ST datasheet, 25AA256-E/ST pinout, 25AA256-E/ST application, or 25AA256-E/ST equivalent, key selection criteria include its extended-temperature TSSOP-8 package, 10 MHz max clock at 4.5–5.5 V, low 1 µA standby current, and block-level write protection (none/¼/½/all array).

Technical Context

The 25AA256-E/ST implements a standard SPI Mode 0,0 or Mode 1,1 interface with separate SI (data in) and SO (data out) lines, CS-controlled selection, and HOLD pin for transaction suspension without reset. Its internal architecture includes an 8-bit instruction register, page latches, HV generator for EEPROM programming, and a STATUS register with WIP, WEL, BP0/BP1, and WPEN bits.

Write operations require explicit WREN instruction followed by CS high-to-low transition to initiate internal 5 ms erase/write cycle; reads support sequential addressing with automatic address roll-over at 0x7FFF. Block protection is implemented via nonvolatile BP0/BP1 bits controlling write access to 0–¼–½–full memory segments.

Key Specifications

Pinout & Package

25AA256-E/ST is housed in an 8-lead Thin Shrink Small Outline Package (TSSOP-8), 4.4 mm body width, RoHS-compliant, with gull-wing leads and JEDEC-standard footprint. Pin 1 marked via notch or bevel; pin 1 location confirmed per rotated TSSOP drawing (HOLD on pin 1, VCC on pin 2).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25LC256-I/ST, the 25AA256-E/ST enables 1.8 V operation in battery-powered edge nodes; compared with AT25DF256A-SSH-T, it offers simpler SPI protocol compatibility and deterministic 5 ms write latency - critical for real-time configuration updates.

Availability

25AA256-E/ST is available at Aetrix Electronics and suitable for automotive control modules, industrial PLCs, medical infusion pumps, and smart energy meters requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 25AA256-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 manufacturing and support infrastructure.

The 25AA256-E/ST belongs to Microchip's serial EEPROM product line, designed specifically for robust, low-power, SPI-based nonvolatile storage in automotive, industrial, and medical applications demanding AEC-Q100 qualification and extended temperature operation.

FAQ

What is the maximum clock frequency supported by the 25AA256-E/ST across its full voltage range?

The 25AA256-E/ST supports up to 10 MHz at VCC = 4.5–5.5 V, 5 MHz at VCC = 2.5–4.5 V, and 3 MHz at VCC = 1.8–2.5 V. These values are specified in Table 1-2 AC Characteristics and reflect guaranteed timing margins across the full –40°C to +125°C operating range. The 25AA256-E/ST must be clocked within these limits to ensure reliable instruction decoding and data transfer integrity.

How does the HOLD pin function during an active SPI transaction on the 25AA256-E/ST?

The HOLD pin on the 25AA256-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 returned high while SCK remains low; the 25AA256-E/ST then continues from the exact bit position where HOLD was asserted - enabling safe interrupt handling in time-critical microcontroller systems.

Can the 25AA256-E/ST be used as a direct replacement for the 25LC256-I/ST in an existing design?

The 25AA256-E/ST is pin-compatible and functionally identical to the 25LC256-I/ST in all respects except supply voltage range: the 25AA256-E/ST operates down to 1.8 V, while the 25LC256-I/ST requires minimum 2.5 V. If the host system supplies ≥2.5 V, the 25AA256-E/ST can be substituted without layout or firmware changes; however, its extended voltage range adds flexibility for future low-power revisions of the 25AA256-E/ST design.

What write protection mechanisms are implemented in the 25AA256-E/ST?

The 25AA256-E/ST implements three-tier write protection: (1) software-controlled BP0/BP1 bits in the STATUS register for 0/¼/½/all array segmentation; (2) hardware WP pin enabled only when WPEN bit = 1; and (3) power-on reset of the write-enable latch. All mechanisms operate independently - for example, WP pin low blocks STATUS register writes even if BP bits permit array writes, ensuring defense-in-depth against unintended modification of the 25AA256-E/ST.

Is the 25AA256-E/ST qualified for automotive applications, and what evidence supports this claim?

Yes, the 25AA256-E/ST is explicitly AEC-Q100 Qualified for Extended Temperature (Grade 1: –40°C to +125°C), as stated in the Device Selection Table and confirmed in Section 1.0 Electrical Characteristics. This qualification includes stress testing for temperature cycling, humidity bias, and ESD (>4 kV HBM), with full parametric validation across the extended range - making the 25AA256-E/ST suitable for engine control, transmission, and ADAS subsystems where reliability is mandated.