AT24C256B-TH-B Equivalent & Substitute Parts

Part Overview

The AT24C256B-TH-B is a 256Kbit EEPROM memory IC with I2C interface manufactured by Microchip Technology. This part operates at 1 MHz clock frequency with 550 ns access time, packaged in 8-TSSOP surface mount configuration. The product status is obsolete, making substitute parts necessary for new designs and ongoing production requirements. Equivalent and substitute parts maintain the same memory capacity, interface protocol, and package form factor while offering active product status and improved availability.

Key Parameters

Parameter	Value
Memory Size	256Kbit
Memory Organization	32K x 8
Memory Interface	I2C
Clock Frequency	1 MHz
Access Time	550 ns
Write Cycle Time	5ms
Voltage Supply Range	1.8V ~ 5.5V
Operating Temperature	-40°C ~ 85°C
Package / Case	8-TSSOP (0.173", 4.40mm Width)
Mounting Type	Surface Mount
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution for the AT24C256B-TH-B is determined by the following critical parameters:

Primary Compatibility Criteria:

Memory Size: 256Kbit (fixed requirement)
Memory Organization: 32K x 8 (fixed requirement)
Memory Interface: I2C (fixed requirement)
Package / Case: 8-TSSOP (fixed requirement)
Mounting Type: Surface Mount (fixed requirement)

Secondary Performance Criteria:

Clock Frequency: 1 MHz (matches original specification)
Access Time: 550 ns or faster (550 ns or lower values are acceptable)
Voltage Supply Range: Must encompass or exceed 1.8V ~ 5.5V
Operating Temperature: Must support -40°C ~ 85°C minimum

Substitute parts are grouped into two categories:

Category 1 - Direct Functional Equivalents (1 MHz Operation): Parts operating at 1 MHz clock frequency with matching or superior access time specifications. These parts provide identical performance characteristics to the original AT24C256B-TH-B.

Category 2 - Compatible Alternatives (400 kHz Operation): Parts operating at 400 kHz clock frequency. These parts are functionally compatible in applications where the reduced clock speed does not impact system requirements. All other parameters remain compatible.

Parameter Comparison

Part Number	Manufacturer	Memory Size	Clock Frequency	Access Time (ns)	Voltage Supply	Operating Temp	Package	Product Status
AT24C256B-TH-B	Microchip Technology	256Kbit	1 MHz	550	1.8V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Obsolete
24AA256-I/ST	Microchip Technology	256Kbit	400 kHz	900	1.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Active
24AA256-E/ST	Microchip Technology	256Kbit	400 kHz	900	1.7V ~ 5.5V	-40°C ~ 125°C	8-TSSOP	Active
24AA256UID-I/ST	Microchip Technology	256Kbit	400 kHz	900	1.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Active
24FC256-I/ST	Microchip Technology	256Kbit	1 MHz	400	1.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Active
AT24C256C-XHL-B	Microchip Technology	256Kbit	1 MHz	550	1.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Active
BR24G256FVT-3AGE2	Rohm Semiconductor	256Kbit	1 MHz	Not specified	1.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP-B	Active
BR24G256FVT-3GE2	Rohm Semiconductor	256Kbit	400 kHz	Not specified	1.6V ~ 5.5V	-40°C ~ 85°C	8-TSSOP-B	Active
BR24T256FVT-WE2	Rohm Semiconductor	256Kbit	400 kHz	Not specified	1.6V ~ 5.5V	-40°C ~ 85°C	8-TSSOP-B	Active
M24256-BFDW6TP	STMicroelectronics	256Kbit	1 MHz	450	1.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Active
M24256-BRDW6P	STMicroelectronics	256Kbit	1 MHz	450	1.8V ~ 5.5V	-40°C ~ 85°C	8-TSSOP	Active

Engineering Selection Recommendations

Primary Recommendation - Direct Equivalent: AT24C256C-XHL-B (Microchip Technology) provides the closest functional match with identical 1 MHz clock frequency and 550 ns access time. This part maintains full compatibility with the original AT24C256B-TH-B specification and carries active product status with ROHS3 compliance.

Performance-Enhanced Alternatives (1 MHz Operation): 24FC256-I/ST, M24256-BFDW6TP, and M24256-BRDW6P all operate at 1 MHz with access times of 400 ns or 450 ns, providing faster performance than the original 550 ns specification. These parts are suitable for applications requiring improved speed performance while maintaining I2C interface compatibility.

Cost-Optimized Alternatives (400 kHz Operation): 24AA256-I/ST, 24AA256-E/ST, 24AA256UID-I/ST, BR24G256FVT-3GE2, and BR24T256FVT-WE2 operate at 400 kHz clock frequency. These parts are suitable for applications where reduced clock speed does not impact system timing requirements. All maintain 256Kbit capacity and I2C interface compatibility.

Extended Temperature Option: 24AA256-E/ST supports operating temperature range of -40°C ~ 125°C, providing extended high-temperature capability for applications requiring operation beyond the standard -40°C ~ 85°C range.

All recommended substitute parts maintain ROHS3 compliance and are currently in active production status.

Frequently Asked Questions (FAQ)

Q: Can I use a 400 kHz part as a substitute for the 1 MHz AT24C256B-TH-B? A: Yes, if your application does not require 1 MHz clock frequency operation. The 400 kHz parts (24AA256 series, BR24G256FVT-3GE2, BR24T256FVT-WE2) are fully compatible with the same I2C protocol and memory organization. Verify that your system timing requirements accommodate the reduced clock speed.

Q: What is the difference between 8-TSSOP and 8-TSSOP-B packages? A: Both packages are physically compatible with 0.173" width and 4.40mm dimensions, suitable for the same PCB footprints. The -B designation indicates a variant from Rohm Semiconductor. Consult specific manufacturer datasheets for any minor pinout or thermal characteristic differences.

Q: Is the AT24C256C-XHL-B a direct replacement for AT24C256B-TH-B? A: Yes. The AT24C256C-XHL-B matches the original part's 1 MHz clock frequency, 550 ns access time, and 8-TSSOP package. It is the recommended direct equivalent with active product status.

Q: Why do some substitute parts have different voltage supply ranges? A: Voltage supply ranges vary by manufacturer design. The original AT24C256B-TH-B specifies 1.8V ~ 5.5V. Substitute parts with ranges such as 1.7V ~ 5.5V or 1.6V ~ 5.5V provide equal or broader compatibility. Verify your application's supply voltage falls within the selected part's specified range.

Q: Are all substitute parts ROHS3 compliant? A: Yes. All substitute parts listed carry ROHS3 compliance certification, matching the environmental compliance status of the original AT24C256B-TH-B.

Q: What is the significance of access time differences (400 ns vs 450 ns vs 550 ns vs 900 ns)? A: Access time represents the delay from address input to data output availability. Faster access times (400 ns, 450 ns) provide improved performance. Slower access times (900 ns) are still compatible with I2C protocol timing but may not be suitable for applications requiring faster data retrieval. Select based on your system's timing requirements.

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