MCP7940NT-E/SN Real Time Clock (RTC) Equivalent & Substitute Parts

Part Overview

The MCP7940NT-E/SN is a Real Time Clock (RTC) IC manufactured by Microchip Technology, designed for clock/calendar applications with I2C serial interface. This 8-SOIC surface mount device operates across a wide supply voltage range (1.8V to 5.5V) and includes integrated features such as alarm functionality, leap year compensation, square wave output, and 64 bytes of SRAM. The device is actively produced and carries AEC-Q100 automotive qualification with ROHS3 compliance.

Substitute parts are necessary when the primary device becomes unavailable, when design requirements demand alternative package configurations, or when specific performance characteristics (such as reduced power consumption or expanded memory) are required for system optimization.

Key Parameters

Parameter	MCP7940NT-E/SN
Manufacturer	Microchip Technology
Package / Case	8-SOIC (0.154", 3.90mm Width)
Interface	I2C, 2-Wire Serial
Voltage - Supply	1.8V ~ 5.5V
Voltage - Supply, Battery	1.3V ~ 5.5V
Current - Timekeeping (Max)	1.2µA @ 3.3V
Operating Temperature	-40°C ~ 125°C
Memory Size	64B
Time Format	HH:MM:SS (12/24 hr)
Date Format	YY-MM-DD-dd
Features	Alarm, Leap Year, Square Wave Output, SRAM
Product Status	Active
Grade	Automotive
Qualification	AEC-Q100
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution eligibility is determined by the following critical parameters:

Interface Compatibility: All substitute parts must support I2C, 2-Wire Serial protocol to ensure firmware and PCB design compatibility.

Supply Voltage Range: Substitute parts must operate within or encompass the 1.8V to 5.5V supply voltage window. Parts with narrower ranges (such as 1.7V ~ 3.6V) are acceptable only if the application operates within that subset.

Package Compatibility: The 8-SOIC package is the primary form factor. Substitutes in alternative packages (8-TSSOP, 8-UFDFN, 16-SOIC, 16-QFN, or module form factors) are listed as functional equivalents but require PCB redesign.

Time and Date Format: All substitutes must support HH:MM:SS and YY-MM-DD-dd formats to maintain firmware compatibility.

Operating Temperature Range: The MCP7940NT-E/SN operates to 125°C. Substitutes with 85°C maximum ratings are acceptable for applications not requiring extended temperature operation.

Product Status: Active status is preferred; parts marked "Not For New Designs" are listed for reference only and should not be selected for new applications.

Parameter Comparison

Parameter	MCP7940NT-E/SN	1337AGDVGI	AB-RTCMC-32.768KHZ-B5GA-S3-T	AB1805-T3	BU9873NUX-TTR	DS1308U-18+T	DS1337U+T&R	DS1338Z-3+T&R	DS1339AU+	DS1340C-33#T&R	DS1340U-3+
Manufacturer	Microchip	Renesas	Abracon	Abracon	Rohm	Analog Devices	Analog Devices	Analog Devices	Analog Devices	Analog Devices	Analog Devices
Package / Case	8-SOIC	8-TSSOP	10-SMD Module	16-VFQFN	8-UFDFN	8-TSSOP	8-TSSOP	8-SOIC	8-TSSOP	16-SOIC	8-TSSOP
Interface	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire	I2C, 2-Wire
Voltage - Supply	1.8V ~ 5.5V	1.8V ~ 5.5V	1.2V ~ 5.5V	1.7V ~ 3.6V	1.8V ~ 5.5V	1.71V ~ 5.5V	1.8V ~ 5.5V	2.7V ~ 5.5V	1.71V ~ 5.5V	2.97V ~ 5.5V	2.7V ~ 5.5V
Current - Timekeeping (Max)	1.2µA @ 3.3V	0.3µA @ 1.3V~1.8V	0.45µA~0.55µA @ 2V~5V	0.17µA~0.22µA @ 1.8V~3V	1µA~1.35µA @ 3V~5.5V	100µA @ 200µA @ 1.89V~5.5V	0.6µA @ 1.3V~1.8V	200µA @ 3.3V	200µA @ 1.71V~5.5V	150µA @ 5.5V	125µA @ 3.3V
Operating Temperature	-40°C ~ 125°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
Memory Size	64B	—	—	256B	—	56B	—	56B	—	—	—
Time Format	HH:MM:SS (12/24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS (24 hr)	HH:MM:SS:hh	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 (24 hr)	HH:MM:SS (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
Features	Alarm, Leap Year, Square Wave Output, SRAM	Alarm, Leap Year, Square Wave Output	Alarm, Leap Year, Square Wave Output	Alarm, Leap Year, SRAM, Trickle-Charger, Watchdog Timer	Alarm, Leap Year	Leap Year, NVSRAM, Square Wave Output	Alarm, Leap Year, Square Wave Output	Leap Year, NVSRAM, Square Wave Output	Alarm, Leap Year, Square Wave Output, Trickle-Charger	Leap Year, Trickle-Charger	Leap Year, Trickle-Charger
Product Status	Active	Active	Active	Active	Not For New Designs	Active	Active	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Same Package (8-SOIC) Direct Substitutes:

DS1338Z-3+T&R is the closest functional equivalent in the same 8-SOIC package. It maintains I2C interface compatibility, supports 12/24-hour time format with YY-MM-DD-dd date format, and operates across -40°C to 85°C. The supply voltage range (2.7V ~ 5.5V) is narrower than the MCP7940NT-E/SN but covers standard 3.3V and 5V applications. This part is actively produced and ROHS3 compliant.

Alternative Package Substitutes with Reduced Power Consumption:

DS1337U+T&R in 8-TSSOP package offers superior power efficiency (0.6µA timekeeping current at 1.3V~1.8V versus 1.2µA for the MCP7940NT-E/SN) while maintaining full I2C compatibility and 12/24-hour time format. This part is actively produced and suitable for battery-backed applications.

1337AGDVGI (Renesas Electronics) in 8-TSSOP package provides equivalent power efficiency (0.3µA) and full voltage range compatibility (1.8V ~ 5.5V). It is actively produced and ROHS3 compliant.

Extended Memory Substitute:

AB1805-T3 in 16-VFQFN package offers expanded 256-byte memory (versus 64 bytes in the MCP7940NT-E/SN) along with additional features including watchdog timer and trickle-charger. Supply voltage range is 1.7V ~ 3.6V, limiting use to lower voltage systems. This part is actively produced and ROHS3 compliant.

Module-Based Substitute:

AB-RTCMC-32.768KHZ-B5GA-S3-T provides a complete RTC module in 10-SMD form factor with integrated crystal oscillator. Supply voltage range (1.2V ~ 5.5V) exceeds the MCP7940NT-E/SN. This part is actively produced and ROHS3 compliant but requires different PCB footprint.

Not Recommended for New Designs:

BU9873NUX-TTR is marked "Not For New Designs" and should not be selected for new applications despite functional compatibility.

Temperature-Limited Substitutes:

All substitute parts except the MCP7940NT-E/SN operate to maximum 85°C. Applications requiring operation above 85°C must retain the MCP7940NT-E/SN.

Frequently Asked Questions (FAQ)

Q: Can I use DS1338Z-3+T&R as a direct replacement for MCP7940NT-E/SN without PCB changes?

A: Yes. Both parts use 8-SOIC packaging with identical pinout compatibility for I2C clock/calendar applications. Firmware compatibility is maintained through identical time format (HH:MM:SS 12/24 hr) and date format (YY-MM-DD-dd) support. The supply voltage range difference (2.7V ~ 5.5V for DS1338Z versus 1.8V ~ 5.5V for MCP7940NT-E/SN) is not a limitation for standard 3.3V or 5V systems.

Q: Which substitute offers the lowest power consumption?

A: AB1805-T3 provides the lowest timekeeping current at 0.17µA ~ 0.22µA @ 1.8V ~ 3V. However, this part requires 16-VFQFN packaging and operates only to 3.6V maximum supply voltage. For applications requiring 5.5V operation, DS1337U+T&R (0.6µA @ 1.3V~1.8V) or 1337AGDVGI (0.3µA @ 1.3V~1.8V) are preferred.

Q: What is the difference between NVSRAM and SRAM in these RTC devices?

A: SRAM (Static Random Access Memory) in the MCP7940NT-E/SN requires continuous power to retain data. NVSRAM (Non-Volatile Static RAM) in DS1308U-18+T and DS1338Z-3+T&R retains data during power loss. Selection depends on application requirements for data persistence during power-down conditions.

Q: Can I use a substitute with a different package if I redesign the PCB?

A: Yes. Substitutes in alternative packages (8-TSSOP, 16-VFQFN, 16-SOIC, or module form factors) are functionally compatible with the MCP7940NT-E/SN provided that I2C interface, time/date format, and supply voltage requirements are met. PCB redesign is required to accommodate different pin configurations and footprints.

Q: Are all listed substitutes automotive-grade?

A: The MCP7940NT-E/SN carries AEC-Q100 automotive qualification. The substitute parts listed do not explicitly state automotive qualification in the provided specifications. Automotive applications should verify qualification status with manufacturers before selection.

Q: What is the significance of the operating temperature range difference?

A: The MCP7940NT-E/SN operates to 125°C, while all listed substitutes operate to maximum 85°C. Applications requiring operation above 85°C must use the MCP7940NT-E/SN. Standard industrial and commercial applications operating within -40°C to 85°C can use any listed substitute.

Q: Why is BU9873NUX-TTR marked "Not For New Designs"?

A: This designation indicates that the manufacturer (Rohm Semiconductor) is discontinuing or has discontinued active development of this part. While existing inventory may be available, new product designs should not incorporate this part. Use active-status alternatives such as DS1337U+T&R or 1337AGDVGI instead.

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