MCP7940M-I/ST Real Time Clock IC Equivalent & Substitute Parts

Part Overview

The MCP7940M-I/ST is a Real Time Clock (RTC) IC with Clock/Calendar functionality manufactured by Microchip Technology. This device operates as a 64-byte I2C, 2-wire serial interface component in an 8-TSSOP surface mount package. The MCP7940M-I/ST is currently in active product status with 1202 units in stock inventory.

RTC substitution becomes necessary when addressing supply chain constraints, package compatibility requirements, or specific feature requirements such as expanded memory capacity, enhanced power efficiency, or alternative packaging formats. The substitute parts listed below maintain functional equivalence within defined electrical and mechanical parameters.

Key Parameters

Parameter	MCP7940M-I/ST
Manufacturer	Microchip Technology
Category	Clock/Timing
Type	Clock/Calendar
Interface	I2C, 2-Wire Serial
Memory Size	64B
Time Format	HH:MM:SS (12/24 hr)
Date Format	YY-MM-DD-dd
Voltage Supply Range	1.8V ~ 5.5V
Current - Timekeeping (Max)	1µA @ 5.5V
Operating Temperature	-40°C ~ 85°C
Package / Case	8-TSSOP (0.173", 4.40mm Width)
Mounting Type	Surface Mount
Features	Alarm, Leap Year, Square Wave Output, SRAM
RoHS Status	ROHS3 Compliant
Product Status	Active

Substitute Part Grouping Explanation

Substitution eligibility for the MCP7940M-I/ST is determined by the following critical parameters:

Interface Compatibility: All substitute parts must support I2C, 2-wire serial communication protocol.

Time and Date Format: Substitute parts must support HH:MM:SS (12/24 hour) time format and YY-MM-DD-dd date format.

Voltage Supply Range: Substitute parts must operate within or encompass the 1.8V ~ 5.5V supply voltage range of the main part.

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

Mounting Type: Substitute parts must be surface mount devices.

Regulatory Compliance: All substitute parts must maintain ROHS3 compliance and REACH unaffected status.

Package Considerations: While the main part uses 8-TSSOP packaging, substitute parts may utilize alternative 8-pin or equivalent surface mount packages (8-SOIC, 8-MSOP, 8-uMAX/uSOP) that maintain functional compatibility within the specified electrical parameters.

Parameter Comparison

Parameter	MCP7940M-I/ST	AB-RTCMC-32.768KHZ-B5ZE-S3-T	BU9873FVM-GTTR	DS1308U-3+T	DS1337C#	DS1338Z-18+	DS1339AU+T	DS1339U-33+T&R	DS1340Z-3+	DS1342U+T&R	DS1388Z-5+
Manufacturer	Microchip Technology	Abracon LLC	Rohm Semiconductor	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated	Analog Devices Inc./Maxim Integrated
Interface	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	I2C, 2-Wire Serial
Time Format	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)	HH:MM:SS (12/24 hr)	HH:MM:SS (24 hr)	HH:MM:SS (12/24 hr)	HH:MM:SS:hh (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	1.8V ~ 5.5V	1.2V ~ 5.5V	1.8V ~ 5.5V	2.7V ~ 5.5V	1.8V ~ 5.5V	1.71V ~ 5.5V	1.71V ~ 5.5V	2.97V ~ 5.5V	2.7V ~ 5.5V	1.8V ~ 5.5V	4.5V ~ 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	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	8-TSSOP (0.173", 4.40mm Width)	10-SMD Module	8-VSSOP, 8-MSOP (0.110", 2.80mm Width)	8-TSSOP, 8-MSOP (0.118", 3.00mm Width)	16-SOIC (0.295", 7.50mm Width)	8-SOIC (0.154", 3.90mm Width)	8-TSSOP, 8-MSOP (0.118", 3.00mm Width)	8-TSSOP, 8-MSOP (0.118", 3.00mm Width)	8-SOIC (0.154", 3.90mm Width)	8-TSSOP, 8-MSOP (0.118", 3.00mm Width)	8-SOIC (0.154", 3.90mm Width)
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	Active	Active	Not For New Designs	Active	Active	Active	Active	Active	Active	Active	Active

Engineering Selection Recommendations

Primary Substitutes (Active Status): DS1339U-33+T&R, DS1338Z-18+, DS1337C#, DS1342U+T&R, DS1339AU+T, DS1308U-3+T, DS1340Z-3+, and AB-RTCMC-32.768KHZ-B5ZE-S3-T are all in active product status with ROHS3 compliance and REACH unaffected designation. These parts maintain full regulatory alignment with the MCP7940M-I/ST.

Secondary Substitute (Legacy Status): BU9873FVM-GTTR carries a "Not For New Designs" product status designation. While electrically compatible within the specified parameters, this part should be considered only for legacy system maintenance or when supply constraints necessitate its use.

Voltage Supply Consideration: DS1388Z-5+, DS1308U-3+T, and DS1340Z-3+ have minimum supply voltage requirements above 1.8V (4.5V, 2.7V, and 2.7V respectively). These parts are suitable only for applications where the minimum supply voltage meets their specifications.

Module Format Alternative: AB-RTCMC-32.768KHZ-B5ZE-S3-T is supplied as a 10-SMD module format rather than a discrete IC package. This configuration may require different PCB layout considerations compared to the standard 8-pin packages.

Frequently Asked Questions (FAQ)

Q: Can DS1340Z-3+ substitute for MCP7940M-I/ST in all applications?

A: DS1340Z-3+ is electrically compatible within the specified parameters. However, it supports 24-hour time format only, whereas MCP7940M-I/ST supports both 12-hour and 24-hour formats. Applications requiring 12-hour format operation must select an alternative substitute.

Q: What is the significance of the "Not For New Designs" status on BU9873FVM-GTTR?

A: This designation indicates the manufacturer has discontinued active development and support for this part. While functionally compatible, it should not be selected for new product designs. Use only for legacy system maintenance or when no other alternatives are available.

Q: Does package size affect substitution eligibility?

A: Package size affects PCB layout and board space requirements but does not affect electrical substitution eligibility. The MCP7940M-I/ST uses 8-TSSOP packaging. Substitute parts in 8-SOIC, 8-MSOP, or 8-uMAX/uSOP packages maintain the same pin count and electrical interface. AB-RTCMC-32.768KHZ-B5ZE-S3-T uses a 10-SMD module format and requires different PCB integration.

Q: Which substitute offers the lowest timekeeping current consumption?

A: AB-RTCMC-32.768KHZ-B5ZE-S3-T specifies 0.5µA @ 2V ~ 5V, and DS1342U+T&R specifies 0.6µA ~ 0.7µA @ 3V ~ 5V. Both offer lower timekeeping current than the MCP7940M-I/ST at 1µA @ 5.5V.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All listed substitute parts maintain ROHS3 compliance and REACH unaffected status, matching the regulatory compliance profile of the MCP7940M-I/ST.

Q: What is the minimum supply voltage requirement across all substitutes?

A: AB-RTCMC-32.768KHZ-B5ZE-S3-T supports operation down to 1.2V. Most other substitutes support 1.8V minimum. DS1388Z-5+ requires a minimum of 4.5V and is suitable only for higher voltage applications.

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