RX-8581SA:B0 Equivalent & Substitute Parts

Part Overview

The RX-8581SA:B0 is a Real Time Clock (RTC) IC with Clock/Calendar functionality, manufactured by EPSON. It features I2C (2-Wire Serial) interface, alarm capability, and leap year support. The device operates across a wide supply voltage range of 1.8V to 5.5V with extremely low timekeeping current consumption of 0.8µA to 1.2µA at 3V to 5V. The RX-8581SA:B0 is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production requirements. Suitable alternatives must maintain I2C interface compatibility, similar voltage supply ranges, and comparable timekeeping accuracy specifications.

Key Parameters

Parameter	RX-8581SA:B0
Manufacturer	EPSON
Category	Clock/Timing
Type	Clock/Calendar
Interface	I2C, 2-Wire Serial
Voltage Supply Range	1.8V ~ 5.5V
Current - Timekeeping (Max)	0.8µA ~ 1.2µA @ 3V ~ 5V
Operating Temperature	-40°C ~ 85°C
Package / Case	14-SOIC (0.197", 5.00mm Width)
Mounting Type	Surface Mount
Features	Alarm, Leap Year
Time Format	HH:MM:SS (24 hr)
Date Format	YY-MM-DD-dd
RoHS Status	ROHS3 Compliant
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the RX-8581SA:B0 is determined by the following critical parameters:

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

Voltage Supply Range: The RX-8581SA:B0 operates from 1.8V to 5.5V. Substitute parts must support overlapping or equivalent voltage ranges. Parts with narrower ranges (e.g., 2.7V ~ 5.5V or 3.3V ~ 5.5V) are acceptable if the application operates within those bounds.

Operating Temperature: All substitutes must support the -40°C to 85°C range to ensure reliability across industrial and commercial applications.

Timekeeping Current: The RX-8581SA:B0 draws 0.8µA to 1.2µA during timekeeping mode. Substitutes with comparable or lower current consumption are preferred for battery-backed applications.

Package and Mounting: The original 14-SOIC package is surface mount. Substitutes may use different packages (8-TSSOP, 8-SOIC, 16-SOIC, 20-SOIC, 8-DIP) depending on PCB layout constraints and design flexibility.

Core Features: Alarm and leap year support are standard across all listed substitutes. Additional features such as NVSRAM, square wave output, and watchdog timers are available in some alternatives.

Parameter Comparison

Part Number	Manufacturer	Interface	Voltage Supply	Timekeeping Current (Max)	Operating Temp	Package / Case	Features	Product Status
RX-8581SA:B0	EPSON	I2C, 2-Wire Serial	1.8V ~ 5.5V	0.8µA ~ 1.2µA @ 3V ~ 5V	-40°C ~ 85°C	14-SOIC (5.00mm)	Alarm, Leap Year	Obsolete
1339-31DVGI	Renesas Electronics	I2C, 2-Wire Serial	3.3V ~ 5.5V	200µA @ 3.63V ~ 5.5V	-40°C ~ 85°C	8-TSSOP (3.00mm)	Alarm, Leap Year, Square Wave, Trickle-Charger	Active
DS1338C-18#	Analog Devices Inc./Maxim	I2C, 2-Wire Serial	1.71V ~ 5.5V	100µA @ 1.89V	-40°C ~ 85°C	16-SOIC (7.50mm)	Leap Year, NVSRAM, Square Wave Output	Active
DS1338U-18+	Analog Devices Inc./Maxim	I2C, 2-Wire Serial	1.71V ~ 5.5V	100µA @ 1.89V	-40°C ~ 85°C	8-TSSOP (3.00mm)	Leap Year, NVSRAM, Square Wave Output	Active
ISL12022MAIBZ	Renesas Electronics	I2C, 2-Wire Serial	2.7V ~ 5.5V	14µA ~ 15µA @ 3V ~ 5V	-40°C ~ 85°C	20-SOIC (7.50mm)	Alarm, Daylight Savings, Leap Year, SRAM	Active
ISL12026IVZ-T	Renesas Electronics	I2C, 2-Wire Serial	2.7V ~ 5.5V	10µA ~ 20µA @ 2.7V ~ 5.5V	-40°C ~ 85°C	8-TSSOP (4.40mm)	Alarm, Leap Year	Active
M41ST87WMX6TR	STMicroelectronics	I2C, 2-Wire Serial	2.7V ~ 3.6V	0.5mA @ 2.7V ~ 3.6V	-40°C ~ 85°C	28-SOIC (7.50mm)	Alarm, Leap Year, NVSRAM, Square Wave, Supervisor, Watchdog	Active
M41T00SM6F	STMicroelectronics	I2C, 2-Wire Serial	2.7V ~ 5.5V	70µA @ 2.7V ~ 5.5V	-40°C ~ 85°C	8-SOIC (3.90mm)	Leap Year	Active
MCP79402T-I/MS	Microchip Technology	I2C, 2-Wire Serial	1.8V ~ 5.5V	1.2µA (Typ) @ 3.3V	-40°C ~ 85°C	8-TSSOP (3.00mm)	Alarm, Leap Year, Square Wave, SRAM, Unique ID	Active
MCP7940N-I/P	Microchip Technology	I2C, 2-Wire Serial	1.8V ~ 5.5V	1.2µA @ 3.3V	-40°C ~ 85°C	8-DIP (7.62mm)	Alarm, Leap Year, Square Wave, SRAM	Active
MCP7940NT-I/MS	Microchip Technology	I2C, 2-Wire Serial	1.8V ~ 5.5V	1.2µA @ 3.3V	-40°C ~ 85°C	8-TSSOP (3.00mm)	Alarm, Leap Year, Square Wave, SRAM	Active

Engineering Selection Recommendations

Voltage Supply Compatibility: The RX-8581SA:B0 operates from 1.8V to 5.5V. For direct replacement in existing designs, MCP79402T-I/MS, MCP7940N-I/P, and MCP7940NT-I/MS maintain the full 1.8V to 5.5V range. DS1338C-18# and DS1338U-18+ support 1.71V to 5.5V, providing near-equivalent coverage. ISL12022MAIBZ and ISL12026IVZ-T operate from 2.7V to 5.5V and are suitable for applications not requiring sub-2.7V operation. M41ST87WMX6TR is limited to 2.7V to 3.6V and is not recommended as a direct replacement for designs requiring 5.5V operation.

Timekeeping Current Consumption: The RX-8581SA:B0 draws 0.8µA to 1.2µA during timekeeping. MCP79402T-I/MS and MCP7940N-I/P match this specification at 1.2µA typical at 3.3V. ISL12022MAIBZ offers superior efficiency at 14µA to 15µA at 3V to 5V. ISL12026IVZ-T provides 10µA to 20µA consumption. All other alternatives consume higher current during timekeeping mode and are less suitable for battery-backed applications requiring extended runtime.

Package and Mounting Considerations: The original 14-SOIC package is not directly replicated in the substitute list. MCP79402T-I/MS, MCP7940NT-I/MS, DS1338U-18+, and 1339-31DVGI use 8-TSSOP packages, reducing PCB footprint. M41T00SM6F and ISL12026IVZ-T use 8-SOIC packages. DS1338C-18# and ISL12022MAIBZ use larger 16-SOIC and 20-SOIC packages respectively. MCP7940N-I/P is available in 8-DIP for through-hole applications. M41ST87WMX6TR uses a 28-SOIC package. PCB layout modifications may be required depending on package selection.

Product Status and Availability: All substitute parts listed are in active production status, ensuring long-term availability and supply chain stability. The RX-8581SA:B0 is obsolete, making migration to active alternatives necessary for new designs and production continuity.

Compliance and Certifications: All substitute parts are ROHS3 compliant and operate across the -40°C to 85°C industrial temperature range. MCP7940N-I/P and MCP7940NT-I/MS carry AEC-Q100 automotive qualification, suitable for automotive and harsh environment applications.

Frequently Asked Questions (FAQ)

Q: Can MCP79402T-I/MS directly replace the RX-8581SA:B0?

A: MCP79402T-I/MS is functionally compatible. It maintains the 1.8V to 5.5V supply range, supports I2C interface, and provides equivalent timekeeping current consumption at 1.2µA typical at 3.3V. The primary difference is package format: MCP79402T-I/MS uses 8-TSSOP versus the original 14-SOIC. PCB layout modification is required.

Q: Which substitute offers the lowest timekeeping current consumption?

A: ISL12022MAIBZ provides the lowest timekeeping current at 14µA to 15µA at 3V to 5V, followed by ISL12026IVZ-T at 10µA to 20µA. However, both consume significantly more than the RX-8581SA:B0 at 0.8µA to 1.2µA. For battery-backed applications prioritizing minimal power draw, MCP79402T-I/MS or MCP7940NT-I/MS at 1.2µA typical are the closest alternatives.

Q: Is the M41ST87WMX6TR suitable for 5V applications?

A: No. M41ST87WMX6TR operates only from 2.7V to 3.6V and is not suitable for applications requiring 5V operation. It is not recommended as a replacement for the RX-8581SA:B0 in 5V systems.

Q: What are the key differences between DS1338C-18# and DS1338U-18+?

A: Both parts are functionally equivalent with identical electrical specifications (1.71V to 5.5V supply, 100µA timekeeping current, -40°C to 85°C operation). The primary difference is package: DS1338C-18# uses 16-SOIC while DS1338U-18+ uses 8-TSSOP. DS1338U-18+ offers a smaller footprint suitable for space-constrained designs.

Q: Do all substitutes support 24-hour time format?

A: All listed substitutes support both 12-hour and 24-hour time formats, providing flexibility for application requirements. The RX-8581SA:B0 operates exclusively in 24-hour format.

Q: Which substitutes include additional memory for user data?

A: DS1338C-18# and DS1338U-18+ include 56 bytes of NVSRAM. ISL12022MAIBZ provides 128 bytes of SRAM. MCP79402T-I/MS includes 64 bytes of SRAM with unique ID. M41ST87WMX6TR offers 128 bytes of NVSRAM. The RX-8581SA:B0 does not include user-accessible memory.

Q: Are automotive-grade alternatives available?

A: Yes. MCP7940N-I/P and MCP7940NT-I/MS carry AEC-Q100 automotive qualification, suitable for automotive and industrial applications requiring enhanced reliability standards.

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