Last revised: October 29, 2024
Reviewed by: Scott Orlosky, consulting engineer

Image Credit: Allied Electronics, Inc. | Digi-Key Corporation | Microchip Technology, Inc.

Electrically erasable programmable read-only memory (EEPROM) chips are similar to PROM devices, but require that a voltage be applied to be erased. Architecture or status, performance, power characteristics, and packaging information are all important parameters to consider when searching for EEPROM memory chips.

Important Specifications

Architecture or status specifications that are important to consider when searching for EEPROM memory chips include density, number of words, bits per word, bus type, and production status.  Density is the capacity of the memory chip expressed in bits.  Number of words refers to the number of "rows" in the organization of the memory chip.  Each row stores a memory word and connects to a word line (one line of the memory bus) for addressing purposes.  Bits per word refer to the number of "columns" in the organization of the memory chip. Each column connects to a sense / write circuit (a bit), which connects to data input/output lines of the chip. 

Common choices for bus type include parallel, serial, serial-1 wire, serial-2 wire, serial-3 wire, I²C, Microwire, SPI, and serial-uPort. Production status can be active, discontinued or new.  The most popular interfaces are I2C, SPI, and OneWire. Active EEPROM memory chips are available and are currently being manufactured. Discontinued EEPROM memory chips are no longer available from the manufacturer, but may still be found in the supply chain. New devices are either just hitting the market, or are soon to be, as announced by the manufacturer.

Performance Measures

Common performance specifications for EEPROM memory chips include data rate, access time, data retention, endurance, and logic family.  Data rate is the transfer speed in hertz.  This is the number of bits per second that can be moved internally in the chip. Access time is a measurement of time in nanoseconds (ns) used to indicate the speed of memory. Access time is a cycle that begins the moment the CPU sends a request to memory and ends the moment the CPU receives the data it requested.   Specifically, for a synchronous device it is the time, usually in ns, from a clock edge to when data is available at the output of a device. For an asynchronous device it is the time from the initiation of the read cycle to when the data output is available. Data retention is the time (in years) that the memory chip can retain the data without reloading. Endurance is the maximum number of write / read cycles that the chip can support.  Common choices for logic family include L, S, H, LS, AS, ALS, FAST, HC, HCT, AHC, AHCT, FCT, AC, ACT, AQC, ABT, ABTE, ABTH, BCT, BTL, CBT, FB, GTL, GTLP, ALB, LV, LVC, LVCH, ALVC, LVT, LVTZ, ALVCH, LCX, VCX, CBTLV, CMOS (4000), ECL, and TTL. 

Power Usage and Requirements

Important power characteristics specifications to consider when selecting EEPROM memory chips include supply voltage, power dissipation, operating current, and standby current.  Common choices for supply voltage include –5 V, -4.5 V, -3.3 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 2.7 V, 3 V, 3.3 V, 3.6 V, and 5 V.  The power dissipation is the total power consumption of the device. It is generally expressed in watts or milliwatts. The operating current is the minimum current needed for active chip operation. The standby current is the minimum current needed for the operation of the chip while is inactive.  Common package information for EEPROM memory chips includes pin count, screening level, package type, package material, and operating temperature. 

Standards

• MIL-M-38510/165 — Microcircuits, Memory, Digital, CMOS 524, 288 Bit, Electrically Erasable, Programmable Read-Only Memory (EEPROM), Monolithic Silicon
• SMD 5962-87514 — Microcircuit, Memory, Digital, CMOS 8k X 8-Bit EEPROM, Monolithic Silicon

EEPROM FAQs

How is EEPROM different from other types of memory?

EEPROM is non-volatile, meaning it retains its data even when power is turned off. Unlike RAM, which loses data when power is lost, EEPROM can store data indefinitely. It is also different from Flash memory in that it allows data to be written and erased at the byte level rather than in blocks.

What are the common performance measures for EEPROM?

Performance measures often include:

• Endurance: The number of write/erase cycles the EEPROM can handle before failure. For example, some EEPROMs can endure over 100 million cycles.
• Write time: The time it takes to write data to the EEPROM. For instance, a 10-ms delay is required for the charge pump to stabilize after an erase or program operation.

What are the different write modes in EEPROM?

There are three primary write modes:

• Byte Mode: Changes the contents of the array one byte at a time.
• Page Mode: Allows multiple bytes (e.g., up to 128 bytes) to be written simultaneously.
• Block (or Bulk) Mode: Changes the entire array data contents at once 

How is EEPROM accessed and programmed in microcontrollers?

In the HC11 and AVR families of microcontrollers, EEPROM requires a 20 Vpp voltage for erasing and programming, obtained by a charge pump. Before programming, an EEPROM bit must be erased, and a 10-ms delay is required for the charge pump to stabilize. Other microcontrollers may have different specific requirements, although the sequence of steps are similar for similar EEPROMS.

What are the power usage and requirements for EEPROM?

EEPROM typically requires a specific voltage for programming and erasing operations. For instance, a 20 Vpp voltage is needed, and the charge pump's current capability is very low, necessitating a stabilization time’.

How does the charge pump work in EEPROM programming?

The charge pump in EEPROM programming is a component that generates the necessary voltage for erasing and programming the memory cells.

EEPROM programming and erasing require a higher voltage than what is typically supplied to the microcontroller. Specifically, a 20 Vpp voltage is needed for these operations.

The charge pump is an internal circuit within the EEPROM that generates this higher voltage from the lower supply voltage. This is achieved through a series of capacitors and switches that effectively "pump" the voltage up to the required level.

The current capability of the charge pump is very low, which means it cannot supply a large amount of current quickly. As a result, the charge pump requires a stabilization time of around 10 milliseconds after an erase or program operation to ensure the voltage is stable and sufficient for the operation.

Before programming, an EEPROM bit must be erased, which sets the bit to a value of 1. After this, the charge pump generates the necessary voltage to program the bit to the desired value. The 10-ms delay ensures that the charge pump has stabilized and the voltage is adequate for reliable programming.

EEPROM Media Gallery

References

GlobalSpec—Microcontrollers in Practice