Microchip Technology 25LC256XT-I/ST

Overview

25LC256XT-I/ST from Microchip Technology is a 256 Kbit (32,768 × 8) SPI Serial EEPROM with 64-byte page write capability, 10 MHz max clock frequency, and industrial temperature range (–40°C to +85°C). It operates from 2.5V to 5.5V, supports hardware write protection via WP pin and STATUS register, and is used for nonvolatile configuration storage in microcontroller-based systems.

For engineers reviewing the 25LC256XT-I/ST datasheet, 25LC256XT-I/ST pinout, 25LC256XT-I/ST application, or 25LC256XT-I/ST equivalent, key selection criteria include SPI timing compliance at 10 MHz, 64-byte page boundary handling, HOLD pin behavior during interrupt servicing, and block protection granularity (none/¼/½/all array).

Technical Context

The 25LC256XT-I/ST implements a standard SPI Mode 0,0 or Mode 1,1 interface with separate SI (data-in) and SO (data-out) lines, requiring CS, SCK, SI, SO, WP, HOLD, VCC, and VSS. Its internal architecture includes a 32,768-byte EEPROM array, page latches, HV generator, and STATUS register with WIP/WEL/BP0/BP1 bits.

Write operations require explicit WREN instruction followed by CS high-to-low transition to initiate TWC (5 ms max); read operations support sequential addressing with automatic address rollover at 0x7FFF. HOLD pin suspends ongoing transfers without resetting the sequence, provided it's asserted while SCK is low.

Key Specifications

Pinout & Package

25LC256XT-I/ST uses an 8-lead TSSOP package (4.4 mm body width, JEDEC MO-153), marked "25LC256I" with temperature code 'I' and date code. Pin 1 is located at top-left corner with notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25AA256-I/ST, the 25LC256XT-I/ST guarantees operation down to 2.5V (not 1.8V) but maintains identical timing and protection features; versus AT25DF256A-SSH-T, it offers simpler SPI-0/1 compatibility and HOLD functionality at lower density and cost.

Availability

25LC256XT-I/ST is available at Aetrix Electronics and suitable for industrial PLCs, automotive ECUs, medical calibration systems, and consumer appliance settings retention requiring stable component supply over extended production lifecycles.

Supply support for 25LC256XT-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, FPGA, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25LC256 belongs to Microchip's serial EEPROM product line, designed specifically for reliable, low-power, SPI-based nonvolatile storage in resource-constrained embedded systems across industrial, automotive, and medical markets.

FAQ

What is the maximum clock frequency supported by the 25LC256XT-I/ST?

The 25LC256XT-I/ST supports up to 10 MHz SPI clock frequency when VCC is 4.5V to 5.5V. At 2.5V ≤ VCC < 4.5V, max clock drops to 5 MHz; below 2.5V, it is not rated. This is specified in Table 1-2 AC Characteristics and confirmed in the Device Selection Table. The 25LC256XT-I/ST must be operated within these voltage-dependent limits to ensure timing compliance and data integrity.

Does the 25LC256XT-I/ST support page write across address boundaries?

No, the 25LC256XT-I/ST does not support page writes across physical page boundaries. Each page is 64 bytes (addresses 0x0000–0x003F, 0x0040–0x007F, etc.). Attempting a multi-byte write that crosses a 64-byte boundary causes wraparound within the current page, overwriting earlier bytes. This behavior is explicitly documented in Section 2.3 and Figure 2-3. Firmware must validate address alignment before issuing page write commands to the 25LC256XT-I/ST.

How does the HOLD pin function during an active SPI transaction on the 25LC256XT-I/ST?

The HOLD pin on the 25LC256XT-I/ST suspends SPI communication mid-transfer when pulled low while SCK is low. During HOLD, SI, SCK, and SO enter high-impedance states and all input transitions (except CS) are ignored. To resume, HOLD must be raised while SCK remains low. This allows the host MCU to service higher-priority interrupts without restarting the sequence. Timing requirements (THS, THH, THV, THZ) are defined in Table 1-2 for the 25LC256XT-I/ST.

What write protection mechanisms are implemented in the 25LC256XT-I/ST?

The 25LC256XT-I/ST implements three layered protections: (1) Write Enable Latch (WEL) reset on power-up and after each write, requiring WREN instruction; (2) Software-configurable Block Protection (BP0/BP1) for 0%/25%/50%/100% array locking; and (3) Hardware WP pin control enabled only when WPEN bit = 1. These are detailed in Sections 2.4–2.6 and Table 2-3. All mechanisms apply to the 25LC256XT-I/ST and prevent unintended writes during brownout or noise events.

Is the 25LC256XT-I/ST qualified for automotive applications?

Yes, the 25LC256XT-I/ST is AEC-Q100 qualified (Grade 2, –40°C to +105°C ambient), as stated in the Features section and Device Selection Table. Its 'I' temperature grade covers industrial range (–40°C to +85°C), and the AEC-Q100 qualification confirms robustness against thermal cycling, humidity, and vibration per automotive standards. This makes the 25LC256XT-I/ST suitable for under-hood and cabin ECU applications where reliability is critical.