Microchip Technology 25AA256T-E/ST

Overview

25AA256T-E/ST from Microchip Technology Inc. is a 256 Kbit (32,768 × 8) SPI Serial EEPROM with 1.8–5.5 V supply range, 64-byte page write capability, and automotive-grade AEC-Q100 qualification for extended temperature operation (–40°C to +125°C). It features hardware write protection via WP pin and STATUS register control, self-timed 5 ms max write cycles, and 1 µA standby current - deployed in engine control units, industrial sensor nodes, and medical device configuration storage.

For engineers reviewing the 25AA256T-E/ST datasheet, 25AA256T-E/ST pinout, 25AA256T-E/ST application, or 25AA256T-E/ST equivalent, key selection criteria include its 1.8 V minimum VCC support, TSSOP-8 (ST) package compatibility, HOLD pin functionality for SPI bus arbitration, and block-level write protection granularity (none/¼/½/all array).

Technical Context

The 25AA256T-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 for full protocol compliance. Its internal architecture includes an 8-bit instruction register, page latches, and HV generator for EEPROM programming - enabling byte/page writes and STATUS register access without external high-voltage sources.

Write operations require explicit WREN instruction followed by CS high-to-low transition to initiate internal 5 ms erase/write cycle; during this time, RDSR reads return valid WIP bit status while memory reads are blocked. Block protection is controlled nonvolatily via BP0/BP1 bits in the STATUS register, with hardware write-protection enabled only when WP = low AND WPEN = 1.

Key Specifications

Pinout & Package

25AA256T-E/ST is housed in an 8-lead Thin Shrink Small Outline Package (TSSOP-8), marked "ST" in Microchip's packaging nomenclature, with 4.4 mm body width and gull-wing leads compatible with standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25LC256T-E/ST and AT25DF256A-SSH-T, the 25AA256T-E/ST uniquely supports 1.8 V operation and retains full HOLD functionality - making it the only option for ultra-low-power, interrupt-aware SPI designs in automotive and portable medical systems.

Availability

25AA256T-E/ST is available at Aetrix Electronics and suitable for engine control units, industrial sensor nodes, medical infusion pumps, and smart energy meters requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for 25AA256T-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, and Flash-IP solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25AA256T-E/ST belongs to Microchip's 25XX256 family of SPI Serial EEPROMs, engineered for robust nonvolatile data storage in automotive, industrial, and medical applications where extended temperature operation and AEC-Q100 compliance are mandatory.

FAQ

What is the minimum supply voltage required for reliable operation of the 25AA256T-E/ST?

The 25AA256T-E/ST operates reliably from 1.8 V to 5.5 V. At 1.8 V, maximum clock frequency is reduced to 3 MHz, and DC characteristics such as VOL and VIH are adjusted per datasheet Table 1-1. This 1.8 V minimum enables direct integration with low-power microcontrollers like the PIC16LF18326 without level-shifting circuitry - a key advantage over competing EEPROMs with 2.5 V or higher VCC minima. The 25AA256T-E/ST maintains full instruction set and write protection functionality across its entire voltage range.

How does the HOLD pin function during an active SPI transaction on the 25AA256T-E/ST?

The HOLD pin on the 25AA256T-E/ST suspends SPI communication mid-sequence: when pulled low while SCK is low, it tri-states SO and ignores further SI/SCK transitions, preserving the internal address pointer and instruction state. To resume, HOLD must be returned high while SCK remains low - after which the device continues from the exact point of suspension. This behavior is critical for time-sensitive systems like automotive ECUs, where the host MCU must service CAN interrupts without aborting EEPROM writes. The 25AA256T-E/ST does not reset its state machine or require retransmission upon HOLD release.

Can the 25AA256T-E/ST be used as a direct replacement for the 25LC256T-E/ST in an existing design?

No - the 25AA256T-E/ST and 25LC256T-E/ST are not direct replacements due to differing VCC ranges: the 25AA256T-E/ST supports 1.8–5.5 V, while the 25LC256T-E/ST requires 2.5–5.5 V. If the host system operates below 2.5 V, substituting 25LC256T-E/ST will cause functional failure. Even within 2.5–5.5 V, differences in input threshold voltages (VIL/VIH) and AC timing margins may affect marginal designs. The 25AA256T-E/ST should only replace 25LC256T-E/ST after validation across worst-case voltage, temperature, and timing corners.

What write protection mechanisms are implemented in the 25AA256T-E/ST?

The 25AA256T-E/ST implements three layered write protection mechanisms: (1) a volatile write enable latch reset on power-up and after each WRITE/WRSR command; (2) nonvolatile BP0/BP1 bits controlling quarter/half/full array lock via STATUS register; and (3) hardware WP pin that - when combined with WPEN bit - disables STATUS register writes only. These operate independently: WP pin has no effect on memory writes, and BP bits do not restrict RDSR reads. This multi-level scheme allows flexible security policies - e.g., locking calibration data (upper 1/4) while permitting runtime log writes to lower addresses - all enforced by the 25AA256T-E/ST's internal logic without MCU intervention.

Is the 25AA256T-E/ST qualified for automotive applications, and what standards does it meet?

Yes, the 25AA256T-E/ST is explicitly qualified for automotive use per AEC-Q100 Grade 1 (–40°C to +125°C ambient), with full test documentation in Microchip's DS20001822H datasheet. It meets RoHS Directive 2011/65/EU and is manufactured in TS16949-certified facilities. The "E" suffix denotes Extended temperature grade, and "T-E/ST" packaging confirms tape-and-reel delivery in TSSOP-8 with automotive traceability coding (e.g., YYWW date code and NNN lot trace). This qualification covers thermal cycling, mechanical shock, and HTOL stress testing - validating suitability for powertrain, chassis, and ADAS modules where EEPROM reliability is safety-critical.