RX-8581NB:B PURE SN Real Time Clock (RTC) IC Equivalent & Substitute Parts

Part Overview

The RX-8581NB:B PURE SN is a Real Time Clock (RTC) IC manufactured by EPSON, designed for clock/calendar applications with I2C serial interface. This device operates across a wide supply voltage range of 1.8V to 5.5V and features alarm functionality with ultra-low timekeeping current consumption of 0.8µA to 1.2µA at 3V to 5V. The part is classified as obsolete, making equivalent and substitute components necessary for new designs and ongoing production support.

Key Parameters

Parameter	RX-8581NB:B PURE SN
Manufacturer	EPSON
Category	Clock/Timing
Type	Clock/Calendar
Interface	I2C
Features	Alarm
Voltage - Supply	1.8V ~ 5.5V
Current - Timekeeping (Max)	0.8µA ~ 1.2µA @ 3V ~ 5V
Operating Temperature	-40°C ~ 85°C
Mounting Type	Surface Mount
Package / Case	22-LFDFN
RoHS Status	ROHS3 Compliant
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the RX-8581NB:B PURE SN is determined by the following critical parameters:

Interface Compatibility: I2C serial interface is mandatory for direct substitution
Supply Voltage Range: Minimum 1.8V to 5.5V overlap required for circuit compatibility
Operating Temperature: -40°C to 85°C range must be maintained
Mounting Type: Surface mount technology required
Core Functionality: Clock/Calendar with alarm capability
RoHS Compliance: ROHS3 compliance required for regulatory alignment

Substitute parts are grouped into two categories based on package form factor and feature set:

Group 1 - Compact Packages (8-pin variants): 1337DVGI8, BU9873NUX-TTR, DS1308U-3+, DS1339U-33+T&R, DS1340U-18+, DS1341T+T&R. These parts maintain I2C interface and core RTC functionality in smaller packages.

Group 2 - Enhanced Feature Packages (16-pin variants): AB0805-T3, DS1340C-18#. These parts offer additional features such as SRAM, trickle-charger, and watchdog timer functionality while maintaining I2C compatibility.

Group 3 - Alternative Packages (8-SOIC): BQ32002D, DS1338Z-3+T&R. These parts provide I2C RTC functionality in standard SOIC packaging.

Parameter Comparison

Part Number	Manufacturer	Interface	Voltage Supply	Timekeeping Current (Max)	Operating Temp	Package	Features	Product Status	RoHS
RX-8581NB:B PURE SN	EPSON	I2C	1.8V ~ 5.5V	0.8µA ~ 1.2µA @ 3V ~ 5V	-40°C ~ 85°C	22-LFDFN	Alarm	Obsolete	ROHS3
1337DVGI8	Renesas Electronics	I2C, 2-Wire Serial	1.8V ~ 5.5V	0.6µA @ 1.3V ~ 1.8V	-40°C ~ 85°C	8-TSSOP	Alarm, Leap Year, Square Wave Output	Active	ROHS3
AB0805-T3	Abracon LLC	I2C, 2-Wire Serial	1.7V ~ 3.6V	0.17µA ~ 0.22µA @ 1.8V ~ 3V	-40°C ~ 85°C	16-VFQFN	Alarm, Leap Year, SRAM, Trickle-Charger, Watchdog Timer	Active	ROHS3
BQ32002D	Texas Instruments	I2C, 2-Wire Serial	3V ~ 3.6V	200µA @ 3.3V	-40°C ~ 85°C	8-SOIC	Leap Year, Square Wave Output, Trickle-Charger	Active	ROHS3
BU9873NUX-TTR	Rohm Semiconductor	I2C, 2-Wire Serial	1.8V ~ 5.5V	1µA ~ 1.35µA @ 3V ~ 5.5V	-40°C ~ 85°C	8-UFDFN	Alarm, Leap Year	Not For New Designs	ROHS3
DS1308U-3+	Analog Devices Inc./Maxim Integrated	I2C, 2-Wire Serial	2.7V ~ 5.5V	Not Specified	-40°C ~ 85°C	8-TSSOP	Leap Year, NVSRAM, Square Wave Output	Active	ROHS3
DS1338Z-3+T&R	Analog Devices Inc./Maxim Integrated	I2C, 2-Wire Serial	2.7V ~ 5.5V	200µA @ 3.3V	-40°C ~ 85°C	8-SOIC	Leap Year, NVSRAM, Square Wave Output	Active	ROHS3
DS1339U-33+T&R	Analog Devices Inc./Maxim Integrated	I2C, 2-Wire Serial	2.97V ~ 5.5V	200µA @ 5.5V	-40°C ~ 85°C	8-TSSOP	Alarm, Leap Year, Square Wave Output, Trickle-Charger	Active	ROHS3
DS1340C-18#	Analog Devices Inc./Maxim Integrated	I2C, 2-Wire Serial	1.71V ~ 5.5V	100µA @ 1.89V	-40°C ~ 85°C	16-SOIC	Leap Year, Trickle-Charger	Active	ROHS3
DS1340U-18+	Analog Devices Inc./Maxim Integrated	I2C, 2-Wire Serial	1.71V ~ 5.5V	100µA @ 1.89V	-40°C ~ 85°C	8-TSSOP	Leap Year, Trickle-Charger	Active	ROHS3
DS1341T+T&R	Analog Devices Inc./Maxim Integrated	I2C, 2-Wire Serial	1.8V ~ 5.5V	0.5µA ~ 0.6µA @ 3V ~ 5V	-40°C ~ 85°C	8-WDFN	Alarm, Leap Year, Square Wave Output	Active	ROHS3

Engineering Selection Recommendations

Primary Substitutes (Active Product Status)

For applications requiring direct functional replacement with active product support, the following parts are recommended:

DS1341T+T&R: Offers the closest electrical match to the RX-8581NB:B PURE SN with 1.8V to 5.5V supply range, ultra-low timekeeping current of 0.5µA to 0.6µA at 3V to 5V, and alarm functionality. Active product status ensures long-term availability and support.
1337DVGI8: Provides I2C interface compatibility with 1.8V to 5.5V supply range and active product status. Timekeeping current of 0.6µA at 1.3V to 1.8V demonstrates low-power operation suitable for battery-backed applications.
DS1340U-18+: Supports 1.71V to 5.5V supply range with active product status. Trickle-charger feature provides enhanced battery management capability.

Secondary Substitutes (Limited Voltage Range or Obsolescence)

BU9873NUX-TTR: Maintains 1.8V to 5.5V supply compatibility and alarm functionality but carries "Not For New Designs" status, limiting suitability for new product development.
AB0805-T3: Offers enhanced features including SRAM, trickle-charger, and watchdog timer with active product status. Supply voltage range of 1.7V to 3.6V is narrower than the original part, requiring circuit redesign for applications requiring full 5.5V operation.

Not Recommended

BQ32002D: Supply voltage range of 3V to 3.6V is incompatible with the original part's 1.8V minimum specification, requiring significant circuit modification.

All substitute parts maintain ROHS3 compliance and -40°C to 85°C operating temperature range consistent with the original RX-8581NB:B PURE SN specification.

Frequently Asked Questions (FAQ)

Q: Can I directly replace the RX-8581NB:B PURE SN with any of these substitute parts?

A: Direct replacement depends on package compatibility and circuit board layout. The RX-8581NB:B PURE SN uses a 22-LFDFN package. Substitute parts use different packages (8-TSSOP, 8-SOIC, 8-WDFN, 16-VFQFN, 16-SOIC), requiring PCB redesign. Electrical compatibility is maintained through I2C interface and overlapping supply voltage ranges.

Q: Which substitute part has the lowest power consumption?

A: The AB0805-T3 demonstrates the lowest timekeeping current at 0.17µA to 0.22µA at 1.8V to 3V. However, its supply voltage range (1.7V to 3.6V) is narrower than the original part. The DS1341T+T&R offers comparable ultra-low power consumption of 0.5µA to 0.6µA at 3V to 5V while maintaining the full 1.8V to 5.5V supply range.

Q: What is the significance of "Active" versus "Obsolete" product status?

A: Active product status indicates ongoing manufacturing, availability, and manufacturer support. Obsolete status means the part is no longer manufactured and availability is limited to existing inventory. For new designs, active status parts ensure long-term supply chain reliability.

Q: Are all substitute parts ROHS3 compliant?

A: Yes, all substitute parts listed maintain ROHS3 compliance, consistent with the original RX-8581NB:B PURE SN specification.

Q: Can I use BQ32002D as a substitute if my circuit operates at 3.3V?

A: The BQ32002D operates within the 3V to 3.6V range, making it compatible with 3.3V circuits. However, it cannot support the original part's 1.8V to 5.5V full range. Use BQ32002D only if your application is permanently fixed at 3.3V operation.

Q: What is the difference between I2C and 2-Wire Serial interface?

A: I2C and 2-Wire Serial are equivalent designations for the same communication protocol. All substitute parts use this interface, ensuring software compatibility with the original RX-8581NB:B PURE SN.

Q: Which substitute part offers the most additional features?

A: The AB0805-T3 includes SRAM (256B), trickle-charger, and watchdog timer functionality beyond basic clock/calendar operation. These features provide enhanced system reliability and data retention capability.

Q: Is the DS1338Z-3+T&R suitable for battery-backed operation?

A: Yes, the DS1338Z-3+T&R supports battery backup with supply voltage range of 1.3V to 3.7V for battery operation. It includes NVSRAM for non-volatile data storage during power loss.

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