Microchip Technology 25AA128T-I/ST

Overview

25AA128T-I/ST from Microchip Technology is a 128 Kbit (16,384 × 8) SPI Serial EEPROM with 1.8V–5.5V supply range, 64-byte page write capability, and industrial temperature rating (–40°C to +85°C). It features hardware write protection via WP pin, HOLD suspend functionality, and self-timed 5 ms max write cycles-used for firmware parameter storage in embedded controllers and sensor calibration data retention.

For engineers reviewing the 25AA128T-I/ST datasheet, 25AA128T-I/ST pinout, 25AA128T-I/ST application, or 25AA128T-I/ST equivalent, key selection criteria include VCC compatibility down to 1.8V, SPI clock support up to 10 MHz at 5.5V, page-level write endurance (1M cycles), and TSSOP-8 package suitability for space-constrained PCB layouts.

Technical Context

The 25AA128T-I/ST implements a standard SPI Mode 0,0 interface with separate SI/SO lines, CS-controlled device selection, and HOLD-driven transaction suspension without sequence reset. Its internal architecture includes a status register with WIP/WEL/BP0/BP1 bits, nonvolatile block protection (none/1/4/1/2/all array), and write-enable latch logic requiring explicit WREN before WRITE or WRSR commands.

It supports sequential read across address boundaries with automatic rollover from 3FFFh to 0000h, and enforces strict page-write boundary alignment: writes crossing 64-byte physical page boundaries wrap within the current page. Power-on defaults include standby mode, reset WEL, high-impedance SO, and hardware write protection disabled unless WPEN=1 and WP=low.

Key Specifications

Pinout & Package

8-Lead Thin Shrink Small Outline Package (TSSOP), body width 4.4 mm, lead pitch 0.65 mm, exposed pad optional (connect to VSS or float per design requirements).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25AA128-I/ST, the 25AA128T-I/ST adds AEC-Q100 qualification and tighter lot-level screening for automotive use, while AT25DF041A-SSH-T trades pin compatibility for quad-SPI throughput and 32× greater density-requiring firmware and PCB redesign.

Availability

25AA128T-I/ST is available at Aetrix Electronics and suitable for industrial PLCs, automotive body control modules, medical calibration systems, and smart energy meters requiring stable component supply across multi-year production cycles.

Supply support for 25AA128T-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 components, and memory solutions, headquartered in Chandler, Arizona, with global manufacturing and support infrastructure.

The 25AA128T-I/ST belongs to Microchip's serial EEPROM product line, designed specifically for reliable, low-power nonvolatile data storage in resource-constrained embedded systems requiring SPI interface simplicity and long-term data integrity.

FAQ

What is the maximum SPI clock frequency supported by the 25AA128T-I/ST?

The 25AA128T-I/ST supports up to 10 MHz SPI clock frequency when VCC is 4.5V–5.5V, 5 MHz at 2.5V–4.5V, and 3 MHz at 1.8V–2.5V. These limits are defined in Table 1-2 AC Characteristics and ensure reliable setup/hold timing across voltage grades. The 25AA128T-I/ST must be operated within these bounds to guarantee correct SI sampling and SO output validity.

Does the 25AA128T-I/ST require external pull-up resistors on its SPI lines?

The 25AA128T-I/ST does not require external pull-ups on SI, SO, or SCK for basic operation, as its inputs meet TTL/CMOS thresholds and SO is actively driven. However, CS and WP pins benefit from weak pull-ups (e.g., 10 kΩ to VCC) to prevent floating states during power-up or reset. The 25AA128T-I/ST datasheet specifies VIH ≥ 0.7×VCC and VIL ≤ 0.3×VCC (or 0.2×VCC below 2.7V), making external biasing advisable for noise immunity in noisy environments.

How does the HOLD function behave during an active write cycle in the 25AA128T-I/ST?

The HOLD function is disabled during an internal write cycle (TWC) in the 25AA128T-I/ST. Once a write is initiated (CS rising edge after valid WRITE/WRSR sequence), the device ignores HOLD transitions until the write completes. This prevents interruption of nonvolatile programming. The 25AA128T-I/ST status register WIP bit remains set during this period, and SO enters high-Z; attempting HOLD assertion has no effect until TWC finishes and WIP clears.

Can the 25AA128T-I/ST be used in a 3.3V-only system without level shifting?

Yes, the 25AA128T-I/ST operates fully within 1.8V–5.5V VCC range and supports 3.3V logic levels natively. Its VIH minimum is 0.7×VCC (2.31V at 3.3V), and VIL maximum is 0.3×VCC (0.99V), matching standard 3.3V CMOS thresholds. No level shifting is needed between 3.3V MCUs and the 25AA128T-I/ST, simplifying design and reducing BOM count.

What happens if a page write crosses a 64-byte boundary in the 25AA128T-I/ST?

If a page write command attempts to cross a 64-byte boundary in the 25AA128T-I/ST, data wraps around to the start of the current page instead of advancing to the next page. For example, writing 10 bytes starting at address 3FF6h (within page 0x3F) will store bytes 0–3 at 3FF6h–3FF9h, then bytes 4–9 at 3F00h–3F05h-overwriting prior content. The 25AA128T-I/ST does not auto-align or fault; software must enforce boundary checks before issuing WRITE commands.