RX-8731LC:B3 Equivalent & Substitute Parts

Part Overview

The RX-8731LC:B3 is a Real Time Clock (RTC) IC with Clock/Calendar functionality manufactured by EPSON. This 12-pin surface mount device integrates 80 bits of memory, I2C serial interface, and operates across a wide supply voltage range of 1.7V to 5.5V. The device features alarm capability, EEPROM storage, leap year compensation, and a unique ID function. With a current consumption of 1.4µA to 1.5µA during timekeeping mode at 3V to 5V, it is designed for low-power applications requiring accurate time and date tracking.

The RX-8731LC:B3 is classified as obsolete. Identifying equivalent and substitute parts is necessary to ensure design continuity, maintain supply chain flexibility, and support long-term product availability for applications currently utilizing this component.

Key Parameters

Parameter	RX-8731LC:B3
Manufacturer	EPSON
Category	Clock/Timing
Type	Clock/Calendar
Memory Size	80 bits
Interface	I2C
Time Format	HH:MM:SS (24 hr)
Date Format	YY-MM-DD-dd
Voltage Supply Range	1.7V ~ 5.5V
Current - Timekeeping (Max)	1.4µA ~ 1.5µA @ 3V ~ 5V
Operating Temperature	-40°C ~ 85°C
Mounting Type	Surface Mount
Package	12-TFSOJ (0.094", 2.40mm Width)
Features	Alarm, EEPROM, Leap Year, Unique ID
RoHS Status	ROHS3 Compliant
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the RX-8731LC:B3 is determined by the following critical parameters:

Interface Compatibility: All substitute parts must support I2C or 2-Wire Serial communication to maintain firmware and hardware interface compatibility.

Voltage Supply Range: Substitute parts must operate within or encompass the 1.7V to 5.5V supply range. Parts with narrower ranges (such as 2.7V to 5.5V or 3V to 3.6V) are acceptable if the application's actual supply voltage falls within both ranges.

Time and Date Format: Substitute parts must support 24-hour time format (HH:MM:SS) and YY-MM-DD-dd date format to ensure software compatibility without firmware modification.

Operating Temperature Range: Substitute parts must support the -40°C to 85°C operating temperature range.

Mounting Type: Surface mount packages are required for PCB compatibility.

RoHS Compliance: All substitute parts must maintain ROHS3 compliance to meet regulatory and procurement requirements.

Product Status: Active or recently active parts are preferred over obsolete or not-for-new-designs classifications to ensure long-term availability.

Substitute parts are grouped by package type and feature set. Package variations (8-TSSOP, 8-MSOP, 8-SOIC, 8-UFDFN, 8-DIP) represent different physical form factors but maintain electrical compatibility when interface and voltage parameters align.

Parameter Comparison

Parameter	RX-8731LC:B3	1337DVGI8	1337GDVGI8	BQ32000D	BU9873NUX-TTR	DS1308U-18+T	DS1337+	DS1338Z-3+T&R	DS1339BU+	DS1339U-3+T&R	DS1339U-33+T&R
Manufacturer	EPSON	Renesas	Renesas	Texas Instruments	Rohm	Analog Devices/Maxim	Analog Devices/Maxim	Analog Devices/Maxim	Analog Devices/Maxim	Analog Devices/Maxim	Analog Devices/Maxim
Type	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar
Interface	I2C	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial
Time Format	HH:MM:SS (24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)
Date Format	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd
Voltage Supply Range	1.7V ~ 5.5V	1.8V ~ 5.5V	1.8V ~ 5.5V	3V ~ 3.6V	1.8V ~ 5.5V	1.71V ~ 5.5V	1.8V ~ 5.5V	2.7V ~ 5.5V	1.71V ~ 5.5V	2.7V ~ 5.5V	2.97V ~ 5.5V
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Through Hole	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	12-TFSOJ	8-TSSOP, 8-MSOP	8-TSSOP, 8-MSOP	8-SOIC	8-UFDFN Exposed Pad	8-TSSOP, 8-MSOP	8-DIP	8-SOIC	8-TSSOP, 8-MSOP	8-TSSOP, 8-MSOP	8-TSSOP, 8-MSOP
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Active	Active	Active	Not For New Designs	Active	Active	Active	Active	Active	Active

Engineering Selection Recommendations

Primary Substitutes (Active Status, Full Compatibility):

The DS1338Z-3+T&R, DS1339BU+, DS1339U-3+T&R, and DS1339U-33+T&R from Analog Devices/Maxim Integrated are the preferred substitutes. These parts maintain I2C interface compatibility, support 24-hour time format with YY-MM-DD-dd date format, operate within overlapping voltage ranges, and are classified as Active products. All are ROHS3 compliant. The DS1338Z-3+T&R offers 56 bits of NVSRAM memory and is available in 8-SOIC packaging. The DS1339 variants include trickle-charger functionality and are available in 8-TSSOP/8-MSOP packages.

Secondary Substitutes (Active Status, Voltage Range Considerations):

The 1337DVGI8 and 1337GDVGI8 from Renesas Electronics Corporation are Active products with I2C interface and compatible time/date formats. Both operate at 1.8V to 5.5V, which encompasses most applications using the RX-8731LC:B3 at 3V to 5V. These parts are available in 8-TSSOP and 8-MSOP packages respectively.

The DS1308U-18+T from Analog Devices/Maxim Integrated is an Active product with 56 bits of NVSRAM, I2C interface, and operates at 1.71V to 5.5V. It is available in 8-TSSOP/8-MSOP packaging.

The DS1337+ is an Active product available in 8-DIP through-hole packaging, suitable for applications requiring through-hole mounting instead of surface mount.

Conditional Substitutes (Voltage Range Limitations):

The BQ32000D from Texas Instruments is an Active product with I2C interface and 24-hour time format. However, its supply voltage range is limited to 3V to 3.6V, making it suitable only for applications operating within this narrower range. It is available in 8-SOIC packaging.

Not Recommended for New Designs:

The BU9873NUX-TTR from Rohm Semiconductor is classified as Not For New Designs. While it meets interface and format requirements, its product status restricts its use to legacy applications or where existing inventory must be consumed.

Frequently Asked Questions (FAQ)

Q: Can the DS1338Z-3+T&R directly replace the RX-8731LC:B3 without firmware changes?

A: The DS1338Z-3+T&R supports I2C interface, 24-hour time format, and YY-MM-DD-dd date format, matching the RX-8731LC:B3 core functionality. However, register mapping and command sequences may differ between manufacturers. Firmware validation is required to confirm compatibility with existing software.

Q: What is the primary difference between the DS1339 variants (DS1339BU+, DS1339U-3+T&R, DS1339U-33+T&R)?

A: All three DS1339 variants share the same core RTC functionality and I2C interface. The differences are in packaging format (tube vs. tape & reel), voltage supply range specifications (1.71V to 5.5V, 2.7V to 5.5V, or 2.97V to 5.5V), and maximum timekeeping current (200µA, 150µA, or 200µA respectively). Select based on your application's actual supply voltage and packaging requirements.

Q: Why is the BQ32000D not recommended as a primary substitute?

A: The BQ32000D operates at 3V to 3.6V supply voltage, which is narrower than the RX-8731LC:B3 range of 1.7V to 5.5V. It is suitable only for applications confirmed to operate within the 3V to 3.6V window. Additionally, its maximum timekeeping current is 100µA, significantly higher than the RX-8731LC:B3 at 1.4µA to 1.5µA.

Q: Are the Renesas 1337DVGI8 and 1337GDVGI8 suitable for low-power applications?

A: Both Renesas parts consume 0.6µA at 1.3V to 1.8V during timekeeping, which is lower than the RX-8731LC:B3. However, at higher voltages (3V to 5V), their timekeeping current specifications are not provided in the available data. Confirm power consumption specifications with the manufacturer for your specific operating voltage.

Q: What packaging considerations apply when selecting a substitute?

A: The RX-8731LC:B3 uses 12-TFSOJ packaging. Most substitutes use smaller 8-pin packages (8-TSSOP, 8-MSOP, 8-SOIC, or 8-UFDFN). This requires PCB redesign. The DS1337+ is available in 8-DIP through-hole packaging, which differs from the surface mount requirement of the original part. Verify PCB layout compatibility before selection.

Q: Are all substitute parts ROHS3 compliant?

A: Yes, all listed substitute parts are ROHS3 compliant, matching the compliance status of the RX-8731LC:B3.

Q: Which substitute offers the best long-term availability?

A: The DS1339 variants from Analog Devices/Maxim Integrated and the DS1338Z-3+T&R are classified as Active products with high inventory levels (3,300 to 5,432 pieces reported). These represent the most reliable choices for long-term supply chain continuity.

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