RX-8581SA:B3:ROHS Equivalent & Substitute Parts

Part Overview

The RX-8581SA:B3:ROHS is a Real Time Clock (RTC) IC with Clock/Calendar functionality manufactured by EPSON. This device integrates I2C (2-Wire Serial) interface for timekeeping and date management in a 14-SOIC surface mount package. The part is currently classified as obsolete, making equivalent and substitute parts necessary for ongoing system support and new design alternatives.

The RX-8581SA:B3:ROHS operates across a wide supply voltage range (1.8V to 5.5V) with ultra-low timekeeping current consumption, making it suitable for battery-backed applications. Its feature set includes alarm functionality and leap year compensation.

Key Parameters

Parameter	Value
Manufacturer	EPSON
Part Number	RX-8581SA:B3:ROHS
Category	Clock/Timing
Type	Clock/Calendar
Interface	I2C, 2-Wire Serial
Package / Case	14-SOIC (0.209", 5.30mm Width)
Voltage - Supply	1.8V ~ 5.5V
Current - Timekeeping (Max)	0.8µA ~ 1.2µA @ 3V ~ 5V
Operating Temperature	-40°C ~ 85°C
Time Format	HH:MM:SS (24 hr)
Date Format	YY-MM-DD-dd
Features	Alarm, Leap Year
Mounting Type	Surface Mount
RoHS Status	ROHS3 Compliant
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the RX-8581SA:B3:ROHS is determined by the following critical parameters:

Interface Compatibility: I2C (2-Wire Serial) protocol is mandatory
Time/Date Format: HH:MM:SS (24 hr) and YY-MM-DD-dd format support
Supply Voltage Range: Minimum 1.8V to 5.5V operation capability
Timekeeping Current: Ultra-low current consumption (typically under 2µA)
Operating Temperature: -40°C to 85°C range
Mounting Type: Surface mount technology
RoHS Compliance: ROHS3 compliant status
Features: Alarm and Leap Year functionality

Substitute parts are grouped into two categories based on package compatibility:

Category A - Smaller Packages (8-pin variants): Parts with reduced pin counts but equivalent or superior electrical specifications. These require PCB layout redesign due to different package footprints.

Category B - Larger Packages (14-20 pin variants): Parts with additional features or memory that maintain I2C interface compatibility but may require firmware adaptation.

Parameter Comparison

Parameter	RX-8581SA:B3:ROHS	BU9873FVM-GTTR	DS1341T+	DS1341U+	ISL12022IBZ-T7A
Manufacturer	EPSON	Rohm Semiconductor	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Renesas Electronics Corporation
Interface	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial	I2C, 2-Wire Serial
Voltage - Supply	1.8V ~ 5.5V	1.8V ~ 5.5V	1.8V ~ 5.5V	1.8V ~ 5.5V	2.7V ~ 5.5V
Time Format	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)
Date Format	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd
Features	Alarm, Leap Year	Alarm, Leap Year	Alarm, Leap Year, Square Wave Output	Alarm, Leap Year, Square Wave Output	Alarm, Daylight Savings, Leap Year, SRAM
Current - Timekeeping (Max)	0.8µA ~ 1.2µA @ 3V ~ 5V	1µA ~ 1.35µA @ 3V ~ 5.5V	0.5µA ~ 0.6µA @ 3V ~ 5V	0.5µA ~ 0.6µA @ 3V ~ 5V	14µA ~ 15µA @ 3V ~ 5V
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 85°C
Package / Case	14-SOIC (0.209", 5.30mm Width)	8-VSSOP, 8-MSOP (0.110", 2.80mm Width)	8-WDFN Exposed Pad	8-TSSOP, 8-MSOP (0.118", 3.00mm Width)	8-SOIC (0.154", 3.90mm Width)
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Not For New Designs	Active	Active	Active

Engineering Selection Recommendations

For Direct Replacement (Minimal Redesign)

BU9873FVM-GTTR from Rohm Semiconductor provides the closest electrical match to the RX-8581SA:B3:ROHS with identical supply voltage range (1.8V ~ 5.5V), matching timekeeping current specifications, and equivalent feature set (Alarm, Leap Year). However, this part is classified as "Not For New Designs," limiting its suitability for long-term production. The 8-MSOP package requires PCB layout modification.

For Active Production (Recommended)

DS1341T+ and DS1341U+ from Analog Devices Inc./Maxim Integrated are active products with superior timekeeping current performance (0.5µA ~ 0.6µA), full supply voltage compatibility (1.8V ~ 5.5V), and additional Square Wave Output feature. Both maintain I2C interface and operating temperature range. DS1341T+ uses 8-WDFN package; DS1341U+ uses 8-TSSOP/MSOP package. Both are ROHS3 compliant and actively supported.

For Extended Memory Applications

ISL12022IBZ-T7A from Renesas Electronics Corporation offers 128B SRAM memory, Daylight Savings feature, and active product status. Supply voltage range is 2.7V ~ 5.5V (narrower than original), and timekeeping current is higher (14µA ~ 15µA). This part is suitable when additional memory and calendar features are required, with acceptance of higher power consumption and minimum supply voltage constraint.

Frequently Asked Questions (FAQ)

Q: Can I use an 8-pin substitute in place of the 14-pin RX-8581SA:B3:ROHS without firmware changes?

A: Pin-count reduction requires PCB layout redesign. However, I2C interface compatibility means firmware modifications are typically minimal if the substitute maintains identical I2C protocol and register mapping. Consult the substitute part datasheet for register compatibility.

Q: What is the primary difference between DS1341T+ and DS1341U+ packages?

A: DS1341T+ uses 8-WDFN (3x3mm) package with exposed pad for thermal management. DS1341U+ uses 8-TSSOP/MSOP (0.118", 3.00mm Width) package. Both have identical electrical specifications and I2C interface. Package selection depends on PCB space constraints and thermal requirements.

Q: Why does ISL12022IBZ-T7A have higher timekeeping current than the original part?

A: ISL12022IBZ-T7A includes 128B SRAM memory and Daylight Savings functionality, which contribute to higher current consumption (14µA ~ 15µA versus 0.8µA ~ 1.2µA). This trade-off is acceptable for applications requiring extended memory and calendar features.

Q: Is the minimum supply voltage of 2.7V for ISL12022IBZ-T7A a compatibility issue?

A: Yes. If your system operates below 2.7V, ISL12022IBZ-T7A is not suitable. DS1341T+ and DS1341U+ maintain the original 1.8V minimum, making them better choices for low-voltage applications.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All listed substitute parts are ROHS3 compliant, matching the environmental compliance of the original RX-8581SA:B3:ROHS.

Q: Which substitute has the lowest power consumption?

A: DS1341T+ and DS1341U+ both offer the lowest timekeeping current at 0.5µA ~ 0.6µA @ 3V ~ 5V, which is superior to the original part's 0.8µA ~ 1.2µA specification.

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