DS1688S Real Time Clock IC - Equivalent & Substitute Parts

Part Overview

The DS1688S is a Real Time Clock (RTC) IC with integrated clock/calendar functionality manufactured by Analog Devices Inc./Maxim Integrated. This device operates as a parallel interface RTC with alarm, leap year, square wave output, and unique ID features in a 28-SOIC surface mount package. The DS1688S is classified as obsolete, making equivalent substitute parts necessary for ongoing system support and new design implementations. Substitute parts must maintain functional compatibility across clock/calendar operations, parallel interface architecture, and operating temperature ranges while accommodating packaging and voltage supply variations.

Key Parameters

Parameter	DS1688S Specification
Manufacturer	Analog Devices Inc./Maxim Integrated
Category	Clock/Timing
Type	Clock/Calendar
Interface	Parallel
Memory Size	114B
Time Format	HH:MM:SS (12/24 hr)
Date Format	YY-MM-DD
Features	Alarm, Leap Year, Square Wave Output, Unique ID
Voltage - Supply	2.7V ~ 3.3V, 4.5V ~ 5.5V
Operating Temperature	0°C ~ 70°C
Mounting Type	Surface Mount
Package / Case	28-SOIC (0.337", 8.56mm Width)
Product Status	Obsolete
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution logic for the DS1688S is based on the following critical parameters that determine functional and physical compatibility:

Primary Compatibility Criteria:

Parallel interface architecture (required for direct pin-level compatibility)
Clock/Calendar functionality with time and date tracking
Operating temperature range of 0°C ~ 70°C (minimum requirement)
28-pin package configuration
Alarm and leap year support

Secondary Compatibility Considerations:

Voltage supply ranges (dual-voltage or single-voltage operation)
Mounting type (surface mount vs. through-hole)
Memory capacity and timekeeping current specifications
RoHS and regulatory compliance status

The three substitute parts listed below maintain core functional compatibility through parallel interface operation and clock/calendar architecture. Variations in package type (TSSOP vs. DIP), voltage supply ranges, and mounting methods reflect design flexibility for different application requirements while preserving RTC functionality.

Parameter Comparison

Parameter	DS1688S	BQ4802LYPWR	M48T08-100PC1	M48T18-100PC1
Manufacturer	Analog Devices Inc./Maxim Integrated	Texas Instruments	STMicroelectronics	STMicroelectronics
Category	Clock/Timing	Clock/Timing	Clock/Timing	Clock/Timing
Type	Clock/Calendar	Clock/Calendar	Clock/Calendar	Clock/Calendar
Interface	Parallel	Parallel	Parallel	Parallel
Time Format	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	YY-MM-DD-dd	YY-MM-DD-dd	YY-MM-DD-dd
Features	Alarm, Leap Year, Square Wave Output, Unique ID	Alarm, Daylight Savings, Leap Year, Supervisor, Watchdog Timer	Leap Year, Watchdog Timer	Leap Year, Watchdog Timer
Voltage - Supply	2.7V ~ 3.3V, 4.5V ~ 5.5V	2.7V ~ 3.6V	4.75V ~ 5.5V	4.5V ~ 5.5V
Operating Temperature	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Mounting Type	Surface Mount	Surface Mount	Through Hole	Through Hole
Package / Case	28-SOIC (0.337", 8.56mm Width)	28-TSSOP (0.173", 4.40mm Width)	28-DIP Module (0.600", 15.24mm)	28-DIP Module (0.600", 15.24mm)
Product Status	Obsolete	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

BQ4802LYPWR (Texas Instruments)

The BQ4802LYPWR is an active product with ROHS3 compliance, offering enhanced feature set including daylight savings, supervisor, and watchdog timer functions. This part maintains surface mount configuration with 28-TSSOP packaging, suitable for applications requiring compact form factor. Voltage supply range of 2.7V ~ 3.6V with battery backup support (2.4V ~ 4V) provides flexibility for low-power applications. Timekeeping current specification of 1.5mA typical at 2.7V ~ 3.6V enables efficient battery operation. Selection of this part is appropriate for new designs prioritizing regulatory compliance and extended feature support.

M48T08-100PC1 (STMicroelectronics)

The M48T08-100PC1 is an active Timekeeper® series product with ROHS3 compliance, featuring through-hole 28-DIP packaging for applications requiring traditional PCB mounting. Voltage supply range of 4.75V ~ 5.5V restricts this part to 5V system environments. Timekeeping current of 3mA at 4.7V ~ 5.5V reflects higher power consumption compared to low-voltage alternatives. This part is suitable for legacy system replacements and applications where through-hole mounting is required.

M48T18-100PC1 (STMicroelectronics)

The M48T18-100PC1 is an active Timekeeper® series product with ROHS3 compliance, featuring through-hole 28-DIP packaging. Voltage supply range of 4.5V ~ 5.5V provides broader 5V system compatibility compared to M48T08-100PC1. Timekeeping current of 3mA at 4.5V ~ 5.5V maintains consistent power characteristics. This part is suitable for applications requiring through-hole mounting with flexible 5V supply tolerance.

All three substitute parts maintain parallel interface architecture, clock/calendar functionality, and 0°C ~ 70°C operating temperature compatibility with the DS1688S. Product status and RoHS compliance should be evaluated against specific application requirements and regulatory mandates.

Frequently Asked Questions (FAQ)

Q: Can the BQ4802LYPWR directly replace the DS1688S in existing designs?

A: The BQ4802LYPWR maintains parallel interface and clock/calendar functionality required for RTC operation. However, package type differs (28-TSSOP vs. 28-SOIC), requiring PCB layout modification. Voltage supply range (2.7V ~ 3.6V) is narrower than DS1688S dual-voltage support, necessitating verification of system supply voltages. Pin-level compatibility must be confirmed through datasheet comparison before implementation.

Q: What are the key differences between the M48T08-100PC1 and M48T18-100PC1?

A: Both parts are STMicroelectronics Timekeeper® series devices with identical 28-DIP through-hole packaging and ROHS3 compliance. Primary difference is voltage supply range: M48T08-100PC1 operates at 4.75V ~ 5.5V, while M48T18-100PC1 operates at 4.5V ~ 5.5V. The M48T18-100PC1 provides broader supply tolerance for 5V systems with tighter lower voltage limit. Both maintain 3mA timekeeping current and identical operating temperature range.

Q: Why does the DS1688S require substitution?

A: The DS1688S is classified as obsolete, indicating discontinued manufacturing and limited availability. Substitute parts ensure continued system support, maintenance capability, and new design implementation using active, readily available components. All listed substitutes maintain core RTC functionality while offering improved regulatory compliance through ROHS3 certification.

Q: Are there packaging considerations when selecting a substitute?

A: Yes. The DS1688S uses surface mount 28-SOIC packaging. The BQ4802LYPWR maintains surface mount configuration (28-TSSOP) with smaller footprint. The M48T08-100PC1 and M48T18-100PC1 use through-hole 28-DIP packaging, requiring different PCB mounting approach. Packaging selection depends on application PCB design, available board space, and manufacturing capabilities.

Q: What voltage supply considerations apply to substitute selection?

A: The DS1688S supports dual-voltage operation (2.7V ~ 3.3V and 4.5V ~ 5.5V). The BQ4802LYPWR operates at 2.7V ~ 3.6V with battery backup, suitable for low-power applications. The M48T08-100PC1 and M48T18-100PC1 operate at 5V supply ranges only (4.75V ~ 5.5V and 4.5V ~ 5.5V respectively). System supply voltage must be verified to ensure substitute part compatibility.

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