DS32C35-33# Real Time Clock IC Equivalent & Substitute Parts

Part Overview

The DS32C35-33# is a Real Time Clock (RTC) IC with Clock/Calendar functionality manufactured by Analog Devices Inc./Maxim Integrated. This device integrates 8KB of memory with I2C/2-Wire Serial interface in a 20-SOIC package. The part is classified as Obsolete, making equivalent and substitute components necessary for new designs and ongoing production requirements. Substitute parts must maintain functional compatibility through matching interface protocols, time/date format support, and core RTC features while accommodating package and electrical specification variations.

Key Parameters

Parameter	DS32C35-33#
Manufacturer	Analog Devices Inc./Maxim Integrated
Category	Clock/Timing
Type	Clock/Calendar
Interface	I2C, 2-Wire Serial
Memory Size	8KB
Time Format	HH:MM:SS (12/24 hr)
Date Format	YY-MM-DD-dd
Voltage Supply	2.7V ~ 3.63V
Voltage Supply Battery	2.3V ~ 3.6V
Current Timekeeping (Max)	110µA @ 3.63V
Operating Temperature	0°C ~ 70°C
Package	20-SOIC (0.295", 7.50mm Width)
Mounting Type	Surface Mount
Product Status	Obsolete
RoHS Status	ROHS3 Compliant
MSL Rating	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution logic for the DS32C35-33# is based on the following critical parameters:

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

Time and Date Format: Substitutes must support HH:MM:SS (12/24 hr) time format and YY-MM-DD-dd date format as minimum requirements.

Core Features: Alarm and Leap Year functionality are baseline requirements present in the original part.

Voltage Supply Range: Substitutes must operate within or encompass the 2.7V ~ 3.63V supply range. Parts with extended ranges (1.8V ~ 5.5V) provide broader design flexibility.

Package Consideration: The original 20-SOIC package is large relative to modern RTC offerings. Substitute parts are grouped by package type (8-pin variants, 16-pin variants, 28-pin variants) to reflect available alternatives. Package selection depends on PCB layout constraints and pin count requirements.

Memory Capacity: The original 8KB memory is substantial for RTC applications. Substitutes range from minimal memory (2B SRAM) to equivalent or greater capacity (64B, 1Kb), allowing selection based on application requirements.

Product Status: Active status substitutes ensure long-term availability and supply chain stability compared to the Obsolete original part.

Parameter Comparison

Parameter	DS32C35-33#	1337DVGI	AB-RTCMC-32.768KHZ-AIGZ-S7-T	ISL12058IUZ-T	ISL1208IRT8Z-TK	M41ST85WMX6TR	M41T82RM6F	M41T83RQA6F	MCP7940M-I/SN	MCP79410-I/MS	MCP79410T-I/MNY
Manufacturer	Analog Devices	Renesas	Abracon	Renesas	Renesas	STMicroelectronics	STMicroelectronics	STMicroelectronics	Microchip	Microchip	Microchip
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
Time Format	HH:MM:SS (12/24)	HH:MM:SS (12/24)	HH:MM:SS:hh (24)	HH:MM:SS (12/24)	HH:MM:SS (12/24)	HH:MM:SS:hh (24)	HH:MM:SS:hh (24)	HH:MM:SS:hh (24)	HH:MM:SS (12/24)	HH:MM:SS (12/24)	HH:MM:SS (12/24)
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
Alarm Feature	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Leap Year	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Voltage Supply (V)	2.7 ~ 3.63	1.8 ~ 5.5	1.0 ~ 4.4	1.8 ~ 3.6	2.7 ~ 5.5	2.7 ~ 3.6	2.7 ~ 5.5	2.7 ~ 5.5	1.8 ~ 5.5	1.8 ~ 5.5	1.8 ~ 5.5
Operating Temp (°C)	0 ~ 70	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85	-40 ~ 85
Package	20-SOIC	8-TSSOP	8-WCDFN	8-TSSOP	8-WDFN	28-SOIC	8-SOIC	16-VQFN	8-SOIC	8-TSSOP	8-WFDFN
Product Status	Obsolete	Active	Active	Active	Obsolete	Active	Active	Active	Active	Active	Active
RoHS Status	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3	ROHS3

Engineering Selection Recommendations

For Direct Functional Replacement with Minimal Design Changes:

M41ST85WMX6TR (STMicroelectronics) provides the closest functional match with 44B memory, extended feature set (Supervisor, Watchdog Timer), and 28-SOIC package. This part maintains similar pin density to the original DS32C35-33# and is currently Active in production status.

For Space-Constrained Designs:

MCP7940M-I/SN, MCP79410-I/MS, and MCP79410T-I/MNY (Microchip Technology) offer compact 8-pin packages with Active product status. These parts provide 64B to 1Kb memory capacity and extended voltage supply ranges (1.8V ~ 5.5V), enabling broader application flexibility. MCP79410 variants include Unique ID functionality for enhanced system identification.

For Ultra-Low Power Applications:

AB-RTCMC-32.768KHZ-AIGZ-S7-T (Abracon LLC) delivers the lowest timekeeping current (0.4µA ~ 0.95µA) with extended voltage range (1.0V ~ 4.4V) in an 8-WCDFN package. This part is optimal for battery-powered systems requiring extended operational life.

For Extended Temperature Range:

All substitute parts listed support -40°C ~ 85°C operating temperature, exceeding the original DS32C35-33# specification (0°C ~ 70°C). This provides enhanced reliability for industrial and automotive applications.

Compliance Considerations:

All substitute parts maintain ROHS3 compliance and MSL ratings suitable for standard manufacturing processes. M41ST85WMX6TR carries MSL-3 (168 Hours), requiring controlled storage conditions. All other substitutes carry MSL-1 (Unlimited) ratings for unrestricted handling.

Frequently Asked Questions (FAQ)

Q: Can I directly replace DS32C35-33# with any of these substitutes without PCB modification?

A: Direct pin-for-pin replacement is not possible due to package differences. The DS32C35-33# uses 20-SOIC, while most substitutes use 8-pin or 16-pin packages. PCB layout redesign is required. However, I2C interface compatibility ensures firmware remains unchanged.

Q: Which substitute offers the best compatibility for existing firmware?

A: All substitutes support I2C/2-Wire Serial protocol with identical time format (HH:MM:SS 12/24 hr) and date format (YY-MM-DD-dd) specifications. Firmware compatibility depends on memory access patterns and feature utilization rather than package type. Consult device datasheets for register-level compatibility.

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

A: The original DS32C35-33# operates 0°C ~ 70°C, while substitutes operate -40°C ~ 85°C. Substitutes provide wider temperature margins, improving reliability in extreme environments. For applications within 0°C ~ 70°C, all substitutes remain fully functional.

Q: How does memory capacity affect substitution?

A: The DS32C35-33# provides 8KB memory. Substitutes range from 2B (ISL1208) to 64B/1Kb (MCP79410 series). Smaller memory substitutes require application redesign if the original design utilized the full 8KB capacity. Larger memory substitutes provide drop-in compatibility with additional capacity.

Q: Are there supply chain advantages to selecting specific substitutes?

A: M41ST85WMX6TR, M41T82RM6F, M41T83RQA6F, MCP7940M-I/SN, MCP79410-I/MS, and MCP79410T-I/MNY all carry Active product status with substantial inventory levels (2,705 ~ 15,510 units), ensuring long-term availability. ISL1208IRT8Z-TK is Obsolete, similar to the original part, and should be avoided for new designs.

Q: What packaging considerations apply to high-volume production?

A: 8-pin packages (TSSOP, SOIC, WCDFN, WFDFN) offer superior pick-and-place efficiency and reduced PCB footprint. 16-pin and 28-pin packages provide additional features but require larger board space. Packaging selection should align with production equipment capabilities and thermal management requirements.

Q: Do all substitutes support 12/24-hour time format selection?

A: Most substitutes support 12/24-hour format selection. AB-RTCMC-32.768KHZ-AIGZ-S7-T and M41 series (M41ST85WMX6TR, M41T82RM6F, M41T83RQA6F) operate in 24-hour format only. Verify application requirements before selection.

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