DS1685Q-3+ Equivalent & Substitute Parts

Part Overview

The DS1685Q-3+ is a Real Time Clock (RTC) IC with integrated Clock/Calendar functionality, manufactured by Analog Devices Inc./Maxim Integrated. This device features 242 bytes of NVSRAM, parallel interface, alarm capability, and square wave output in a 28-LCC (J-Lead) surface mount package. The product is classified as obsolete, making equivalent substitute parts necessary for new designs and ongoing production requirements. Substitute parts maintain functional compatibility through equivalent electrical specifications and interface characteristics while offering active product status and improved availability.

Substiute Parts

DS1685Q-3+

Analog Devices Inc./Maxim IntegratedIn Stock: 1152DS1685Q-3+ Datasheet

Current PartRFQ

BQ4802LYDWR

Texas InstrumentsIn Stock: 3828BQ4802LYDWR Datasheet

MFR RecommendedRFQ

BQ4802LYPWR

Texas InstrumentsIn Stock: 28912BQ4802LYPWR Datasheet

MFR RecommendedRFQ

M48T18-100PC1

STMicroelectronicsIn Stock: 1462M48T18-100PC1 Datasheet

MFR RecommendedRFQ

M48T58-70PC1

STMicroelectronicsIn Stock: 1546M48T58-70PC1 Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution logic for the DS1685Q-3+ is based on the following critical parameters:

Electrical Compatibility Criteria:

• Parallel interface architecture
• Time format support (HH:MM:SS with 12/24 hour capability)
• Date format support (YY-MM-DD-dd)
• Operating temperature range (0°C ~ 70°C minimum)
• RoHS3 compliance

Functional Compatibility Criteria:

• Clock/Calendar functionality with alarm capability
• Real Time Clock IC classification
• Supply voltage overlap within acceptable ranges

Package Compatibility Considerations:

• Surface mount packages (28-SOIC, 28-TSSOP) maintain electrical compatibility with the original 28-LCC package
• Through-hole packages (28-DIP) provide functional equivalence with different mounting methodology

The four substitute parts are grouped into two categories: active surface mount alternatives (BQ4802LYDWR, BQ4802LYPWR) and active through-hole alternatives (M48T18-100PC1, M48T58-70PC1). All substitutes maintain parallel interface architecture and support equivalent time/date formats.

Parameter Comparison

Engineering Selection Recommendations

Surface Mount Alternatives (BQ4802LYDWR, BQ4802LYPWR):

The BQ4802LYDWR and BQ4802LYPWR are active Texas Instruments products offering direct functional replacement for the obsolete DS1685Q-3+ in surface mount applications. Both devices maintain 3.3V supply voltage compatibility, parallel interface architecture, and equivalent time/date format support. The BQ4802LYDWR uses 28-SOIC packaging (0.295" width), while the BQ4802LYPWR uses 28-TSSOP packaging (0.173" width). The TSSOP variant provides reduced board footprint. Both are ROHS3 compliant with unlimited moisture sensitivity level (MSL 1). Current consumption is lower than the original part (1.5mA typical vs. 2mA maximum), and battery supply voltage range is broader (2.4V ~ 4V).

Through-Hole Alternatives (M48T18-100PC1, M48T58-70PC1):

The M48T18-100PC1 and M48T58-70PC1 are active STMicroelectronics Timekeeper® series products providing functional replacement in through-hole applications. Both use 28-DIP Module packaging (0.600", 15.24mm). These devices operate at 5V supply voltage (4.5V ~ 5.5V and 4.75V ~ 5.5V respectively), requiring voltage regulation if used in 3.3V systems. Both maintain parallel interface, equivalent date format support, and 0°C ~ 70°C operating temperature range. ROHS3 compliance and unlimited MSL rating are maintained. Current consumption is 3mA at rated supply voltage.

Selection Criteria:

For new designs requiring surface mount implementation with 3.3V supply voltage, the BQ4802 series (LYDWR or LYPWR) is appropriate. For legacy through-hole designs or systems with 5V supply voltage, the M48T series (M48T18-100PC1 or M48T58-70PC1) is appropriate. All substitutes are active products with established supply chains and full RoHS3 compliance.

Frequently Asked Questions (FAQ)

Q: Can the BQ4802LYDWR directly replace the DS1685Q-3+ without PCB redesign?

A: The BQ4802LYDWR maintains electrical and functional compatibility but uses 28-SOIC packaging instead of 28-LCC. PCB footprint redesign is required. The BQ4802LYPWR (28-TSSOP) also requires footprint redesign. Through-hole alternatives (M48T18-100PC1, M48T58-70PC1) require different PCB layout entirely.

Q: What is the primary difference between BQ4802LYDWR and BQ4802LYPWR?

A: Both are functionally identical Texas Instruments BQ4802 devices with equivalent electrical specifications. The primary difference is package type: LYDWR uses 28-SOIC (0.295" width) while LYPWR uses 28-TSSOP (0.173" width). TSSOP provides smaller board footprint.

Q: Are the M48T18-100PC1 and M48T58-70PC1 interchangeable?

A: Both are STMicroelectronics through-hole RTC devices with equivalent functional specifications and 28-DIP Module packaging. The primary difference is supply voltage range: M48T18-100PC1 operates at 4.5V ~ 5.5V while M48T58-70PC1 operates at 4.75V ~ 5.5V. Selection depends on system supply voltage tolerance.

Q: What is the impact of supply voltage differences between the DS1685Q-3+ (2.7V ~ 3.7V) and M48T series (4.5V ~ 5.5V)?

A: The M48T series requires 5V supply voltage and cannot operate directly in 3.3V systems without voltage regulation. The BQ4802 series (LYDWR, LYPWR) maintains 3.3V compatibility (2.7V ~ 3.6V) and is preferred for low-voltage applications.

Q: Do all substitute parts support 12/24 hour time format like the original DS1685Q-3+?

A: The BQ4802LYDWR and BQ4802LYPWR support 12/24 hour time format. The M48T18-100PC1 and M48T58-70PC1 support 24-hour format only. Applications requiring 12-hour format must use the BQ4802 series.

Q: Are all substitute parts RoHS3 compliant?

A: All four substitute parts (BQ4802LYDWR, BQ4802LYPWR, M48T18-100PC1, M48T58-70PC1) are ROHS3 compliant with unlimited moisture sensitivity level (MSL 1).