Microchip Technology AT34C02D-XHM-T

Overview

AT34C02D-XHM-T from Microchip Technology (formerly Atmel) is a JEDEC EE1002/EE1002A-compliant Serial Presence Detect (SPD) EEPROM for DDR/DDR2/DDR3 DIMM modules, providing 2,048-bit (256 × 8) I²C-compatible nonvolatile memory with 1.7V–5.5V operation, permanent/reversible software write protection for lower 128 bytes, and hardware write protection via WP pin.

For engineers reviewing the AT34C02D-XHM-T datasheet, AT34C02D-XHM-T pinout, AT34C02D-XHM-T application, or AT34C02D-XHM-T equivalent, this device delivers SPD-specific timing compliance, dual-layer write protection flexibility, page-write capability (16-byte), 1 MHz I²C support at 5V, and industrial-grade reliability (1M write cycles, 100-year retention) in an 8-lead TSSOP package.

Technical Context

The AT34C02D-XHM-T implements a dedicated SPD EEPROM architecture with hardwired A0–A2 address inputs enabling up to eight devices on one I²C bus, and supports both current-address and random-address read modes with sequential read capability. Its internal 16-page × 16-byte memory organization enables efficient byte and page writes with automatic address roll-over within pages.

Write protection is implemented through three independent mechanisms: hardware-level inhibition via WP pin (full-array lock when tied to VCC), irreversible software lock of addresses 0x00–0x7F, and reversible software lock of the same region using specific command sequences (0x62h/0x66h) with defined A-pin voltage conditions. All protections enforce tWR = 5 ms maximum self-timed write cycle.

Key Specifications

Pinout & Package

AT34C02D-XHM-T is supplied in an 8-lead plastic Thin Shrink Small Outline Package (TSSOP), 4.4 mm body width, with gull-wing leads and NiPdAu lead finish. Pin 1 is marked by a beveled corner or laser mark per JEDEC MO-153.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT24C02D-MAHM-T and STTS222B-TR, the AT34C02D-XHM-T uniquely satisfies JEDEC SPD timing and register map requirements while offering irreversible lower-half write protection - essential for certified DDR memory module designs where SPD integrity is mandatory.

Availability

AT34C02D-XHM-T is available at Aetrix Electronics and suitable for DDR3 DIMM manufacturing, server memory module calibration, and industrial DDR2 memory applications requiring stable component supply, long-term lifecycle support, and JEDEC-compliant SPD functionality.

Supply support for AT34C02D-XHM-T 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 acquired Atmel in 2016 and maintains full product support, documentation, and qualification for legacy Atmel memory devices including the AT34C02D series.

The AT34C02D product line was designed specifically for JEDEC-compliant Serial Presence Detect in DDR/DDR2/DDR3 memory modules, emphasizing SPD timing accuracy, write-protection security, and industrial temperature resilience.

FAQ

What is the primary function of the AT34C02D-XHM-T in memory modules?

The AT34C02D-XHM-T serves as a JEDEC EE1002/EE1002A-compliant Serial Presence Detect (SPD) EEPROM in DDR/DDR2/DDR3 DIMMs. It stores standardized configuration data - including timings, density, vendor ID, and thermal parameters - that the memory controller reads during system boot to initialize and configure the DRAM. Its design ensures strict SPD timing compliance and reliable nonvolatile storage under industrial conditions. The AT34C02D-XHM-T is optimized for this exact role and is not intended as a general-purpose EEPROM.

Does the AT34C02D-XHM-T support I²C fast mode, and what voltage conditions apply?

Yes, the AT34C02D-XHM-T supports I²C fast mode at 1 MHz, but only when VCC is 5.0 V. At 1.7 V or 2.5 V, it operates in standard mode up to 400 kHz. This voltage-dependent speed scaling is explicitly specified in the datasheet and reflects internal timing constraints of the I²C interface logic. The AT34C02D-XHM-T maintains full protocol compliance across both modes, including tSU.STA, tHD.STA, and tBUF requirements per JEDEC and I²C specifications.

How does hardware write protection work on the AT34C02D-XHM-T, and can it be overridden?

Hardware write protection on the AT34C02D-XHM-T is controlled solely by the WP pin: when pulled to VCC, all write operations (including software protection register programming) are disabled, and the device responds with no ACK to any write command. This protection cannot be overridden by software or power cycling - it is strictly pin-driven and active regardless of software protection state. The AT34C02D-XHM-T enforces this behavior per Table 8-4 in the datasheet, ensuring unconditional lockout when WP = VCC.

What is the difference between permanent and reversible software write protection in the AT34C02D-XHM-T?

Permanent software write protection (PSWP), once enabled via command 0x60h, irreversibly locks addresses 0x00–0x7F - the lower 128 bytes - and cannot be cleared even after power loss. Reversible software write protection (RSWP) uses commands 0x62h (set) and 0x66h (clear) and requires specific A-pin voltage conditions (e.g., A0 = VHV); it protects the same 128-byte region but can be disabled. Both operate independently of the WP pin state unless WP = VCC, which overrides all software protection. The AT34C02D-XHM-T implements these two distinct mechanisms to meet SPD security requirements.

Which package type does the AT34C02D-XHM-T use, and what are its key mechanical features?

The AT34C02D-XHM-T uses an 8-lead TSSOP (Thin Shrink Small Outline Package) with 4.4 mm body width, gull-wing leads, and NiPdAu lead finish. Per ordering code "XHM", it conforms to JEDEC MO-153, has 0.65 mm lead pitch, and is rated for industrial temperature (−40°C to +85°C). The "H" denotes green/halogen-free construction and NiPdAu plating; "M" indicates 1.7V–5.5V operation. This package is pin-compatible with other Atmel 2K SPD EEPROMs in TSSOP, enabling drop-in replacement in existing DIMM layouts. The AT34C02D-XHM-T's mechanical drawing is documented as 8X in the datasheet.