Microchip Technology AT27C040-90JU

Overview

AT27C040-90JU from Microchip Technology (formerly Atmel) is a 4 Mb (512K × 8) One-Time Programmable EPROM used for nonvolatile program storage in legacy microprocessor systems. It features 90 ns read access time, 5 V ±10% single-supply operation, and industrial temperature range (–40°C to +85°C). Its dual-line control (CE/OE) enables bus contention-free interfacing with 8-bit data buses in embedded controllers and instrumentation.

For engineers reviewing the AT27C040-90JU datasheet, AT27C040-90JU pinout, AT27C040-90JU application, or AT27C040-90JU equivalent, key selection criteria include verified 90 ns tACC timing, PLCC-32 package compatibility, rapid 100 μs/byte programming, CMOS/TTL I/O compatibility, and integrated product identification code support for automated programming equipment.

Technical Context

The AT27C040-90JU implements a standard OTP EPROM architecture with a 19-bit address bus (A0–A18), 8-bit bidirectional data path (O0–O7), and dedicated VPP pin for 13.0 V programming voltage. Its two-line enable logic (CE active-low, OE active-low) supports high-speed read cycles without bus contention, and its internal identification code (0x1E manufacturer, 0x0B device) is accessed via A9 and A0 under specific VPP conditions.

It operates exclusively in Read, Standby, Rapid Program, PGM Verify, and Product Identification modes - all defined by CE, OE, and VPP states. Programming requires precise 100 μs CE pulses at elevated VCC (6.5 V) and VPP (13.0 V), with up to ten retries per byte during verification; no in-system reprogrammability is supported.

Key Specifications

Pinout & Package

AT27C040-90JU is supplied in a 32-lead plastic J-leaded chip carrier (PLCC) package per JEDEC MS-016 AE, with lead finish matte tin and Pb/halide-free construction. Dimensions: 12.47 mm × 14.98 mm × 3.35 mm (D × E × A).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar OTP EPROM applications.

Compared with AT27C040-70JU, the AT27C040-90JU trades 20 ns slower access for broader timing margin and lower cost; compared with AM27C040-90DC, it offers superior thermal dissipation and board-space efficiency in surface-mount layouts, though requiring PLCC-specific reflow profiles.

Availability

AT27C040-90JU is available at Aetrix Electronics and suitable for industrial control firmware storage, legacy test equipment boot ROM, embedded instrumentation calibration memory, and avionics maintenance diagnostic modules requiring stable component supply across extended product lifecycles.

Supply support for AT27C040-90JU 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 support for legacy Atmel EPROM products including the AT27C040 family. The company specializes in microcontrollers, analog, and nonvolatile memory solutions for industrial and automotive markets.

The AT27C040 series was designed as a drop-in replacement for earlier 27C-series EPROMs, targeting cost-sensitive, high-reliability applications where UV-erasable one-time programmability and industrial temperature tolerance are essential.

FAQ

What is the maximum allowed VPP voltage for programming the AT27C040-90JU?

The absolute maximum VPP voltage for AT27C040-90JU is +14.0 V, but the specified programming voltage is 13.0 V ±0.25 V. Exceeding this range risks permanent damage to the oxide layer or incorrect programming. During normal read operation, VPP must be either floated or tied to VCC (5 V); applying 13 V during read will cause excessive current draw and potential failure. Always follow the timing diagram in Figure 6-4 and Table 6-4 for safe programming.

Can the AT27C040-90JU be used in place of the AT27C040-70JU without design changes?

Yes, the AT27C040-90JU is pin-compatible and functionally identical to the AT27C040-70JU except for read access time (90 ns vs. 70 ns). No PCB layout or schematic changes are needed. However, system timing margins must be re-verified: if the host processor relies on ≤70 ns tACC, substituting AT27C040-90JU may introduce wait states or failures. For most industrial microcontroller systems running below 11 MHz, AT27C040-90JU operates reliably without modification.

Does the AT27C040-90JU support in-system programming (ISP)?

No, the AT27C040-90JU does not support in-system programming. It is a one-time programmable (OTP) EPROM requiring UV-erasable windowed packages for reprogramming - but the AT27C040-90JU uses a plastic PLCC package with no quartz window. Programming must be performed in a dedicated EPROM programmer using 13 V on VPP and 6.5 V on VCC. Once programmed, data is permanently stored and cannot be electrically erased or rewritten.

What decoupling capacitors are required for stable operation of the AT27C040-90JU?

The AT27C040-90JU requires a 0.1 μF high-frequency ceramic capacitor placed between VCC and GND, mounted as close as possible to the device pins. For systems with multiple EPROMs or high-noise environments, a 4.7 μF bulk electrolytic capacitor should also be added near the power entry point. These values are specified in Section 3 ("Switching Considerations") of the datasheet to suppress transient excursions caused by CE switching and ensure compliance with absolute maximum ratings.

How is the manufacturer and device identification code read from the AT27C040-90JU?

The AT27C040-90JU identification code is read by setting VPP = 12.0 V ±0.5 V, holding A1–A18 = VIL, A9 = VH (11.5–12.5 V), and toggling A0: A0 = VIL reads the manufacturer ID (0x1E), while A0 = VIH reads the device ID (0x0B). Both bytes appear on O0–O7 during a standard read cycle with CE and OE asserted. This feature is used by automated programmers to auto-select correct algorithms and voltages before programming the AT27C040-90JU.