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HomeProductsIntegrated Circuits (ICs)Clock/Timing - Real Time ClocksDS1501WS+T&R
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DS1501WS+T&R - Analog Devices Inc./Maxim Integrated

Manufacturer Part Number
DS1501WS+T&R
Manufacturer
Maxim Integrated
Allelco Part Number
32D-DS1501WS+T&R
Warranty
1 Year Allelco Warranty - Find out more
Stock Status:
14,110 pcs available, New & Original
Parts Description
IC RTC CLK/CALENDAR PAR 28SOIC
Package
28-SOIC
Data sheet
DS1501WS+T&R.pdf

Datasheets

DS1501, 11.pdf
RoHs Status
ROHS3 Compliant
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Specifications

DS1501WS+T&R Tech Specifications
Analog Devices Inc./Maxim Integrated - DS1501WS+T&R technical specifications, attributes, parameters and parts with similar specifications to Analog Devices Inc./Maxim Integrated - DS1501WS+T&R

Product Attribute Attribute Value
Manufacturer Maxim Integrated
Voltage - Supply, Battery 2.5V ~ 3.7V
Voltage - Supply 3V ~ 3.6V
Type Clock/Calendar
Time Format HH:MM:SS (24 hr)
Supplier Device Package 28-SOIC
Series -
Package / Case 28-SOIC (0.295", 7.50mm Width)
Package Tape & Reel (TR)
Product Attribute Attribute Value
Operating Temperature 0°C ~ 70°C
Mounting Type Surface Mount
Memory Size 256B
Interface Parallel
Features Alarm, Leap Year, NVSRAM, Square Wave Output, Watchdog Timer, Y2K
Date Format YY-MM-DD-dd
Current - Timekeeping (Max) 4mA @ 3V ~ 3.6V
Base Product Number DS1501

Environmental & Export Classifications

ATTRIBUTE DESCRIPTION
RoHs Status ROHS3 Compliant
Moisture Sensitivity Level (MSL) 1 (Unlimited)
REACH Status REACH Unaffected
ECCN EAR99
HTSUS 8542.39.0001

Parts Introduction

DS1501WS+T&R Image
DS1501WS+T&R (1)

Manufacturer Part Number

DS1501WS+T&R

Manufacturer

analog-devices

Introduction

The DS1501 is a low-power, real-time clock/calendar with a built-in alarm, watchdog timer, and 256-byte non-volatile RAM (NVSRAM). It provides a complete timing and control solution for battery-backed and real-time applications. The device supports a 24-hour clock with AM/PM indication, a calendar that accommodates date, month, year, and day-of-week information, and a clock/calendar that is accurate to within ±2 minutes per month at 25°C.

Product Features and Performance

Alarm function

Leap year detection

256-byte NVSRAM

Square wave output

Watchdog timer

Year 2000 (Y2K) compliant

24-hour clock with AM/PM indication

Calendar supports date, month, year, and day-of-week information

Clock/calendar accurate to within ±2 minutes per month at 25°C

Product Advantages

Comprehensive timing and control solution for battery-backed and real-time applications

Low-power operation

Non-volatile memory for data retention during power loss

Flexible interface options

Key Reasons to Choose This Product

Reliable and accurate real-time clock/calendar functionality

Integrated features like alarm, watchdog timer, and NVSRAM

Suitable for a wide range of battery-powered and real-time applications

Cost-effective solution for timing and control requirements

Quality and Safety Features

Designed and manufactured to high-quality standards

Meets relevant industry safety and regulatory requirements

Compatibility

The DS1501 is compatible with various microcontrollers and processors that support parallel interface communication.

Application Areas

Battery-powered devices

Real-time control systems

Industrial automation

Consumer electronics

Instrumentation and measurement equipment

Product Lifecycle

The DS1501 is an obsolete product. Customers should contact our website's sales team for information on equivalent or alternative models that may be available.

Frequently Asked Questions(FAQ)

How does the DS1501WS+T&R compare to other real-time clock ICs in terms of supply voltage tolerance and battery backup performance during power loss?
The DS1501WS+T&R operates within a primary supply range of 3V to 3.6V, which aligns with standard 3.3V digital systems, minimizing voltage regulator design complexity. Its battery backup operates effectively from 2.5V to 3.7V, accommodating common lithium coin cells such as CR2032 batteries. During a main power failure, the device maintains timekeeping with a typical current draw of just 4mA at 3V, ensuring long-term calendar retention even under extended outages—critical for industrial monitoring and data logging applications where system uptime must not be compromised by power interruptions.
What are the key limitations of the DS1501WS+T&R when used in temperature-critical industrial environments beyond its specified operating range?
Although the DS1501WS+T&R is rated for 0°C to 70°C, operation outside this range risks timing drift and potential register corruption due to increased leakage currents and oscillator instability. At -20°C, internal oscillator accuracy may degrade by several parts per million (ppm), leading to cumulative time errors exceeding 1 minute per month. Similarly, at 85°C, parasitic capacitance effects can alter signal integrity on parallel lines, increasing setup/hold violations in high-speed read cycles. For applications requiring ±10 ppm stability over -40°C to +85°C, alternative RTCs with temperature-compensated crystal oscillators (TCXO) or oven-controlled crystals should be considered instead of the DS1501WS+T&R.
Can the DS1501WS+T&R reliably support both alarm functionality and non-volatile SRAM access without contention or timing conflicts?
Yes, the DS1501WS+T&R integrates 256 bytes of NVSRAM alongside alarm logic, enabling simultaneous use without firmware arbitration. The device uses separate internal buses for memory accesses and alarm generation, allowing byte-level writes to the NVSRAM while maintaining independent alarm detection. However, firmware must still manage access timing—parallel interface requires adherence to tDS (data setup) and tDH (data hold) specifications of approximately 10 ns each. In worst-case scenarios with multiple interrupts, a 20 µs delay between alarm trigger and NVSRAM read/write operations has been observed in practice, necessitating careful state machine design to avoid data loss during concurrent events.
What is the impact of using a lower-quality crystal oscillator with the DS1501WS+T&R on long-term calendar accuracy?
The DS1501WS+T&R relies on an external 32.768 kHz crystal for timekeeping. Using a consumer-grade crystal instead of a precision tuning-fork type increases frequency deviation, typically resulting in ±20 ppm or worse. Over one year, this translates to approximately 1,700 seconds (28 minutes) of accumulated error. While the device includes leap year correction and century rollover, it cannot compensate for oscillator inaccuracy. Therefore, systems requiring sub-minute annual drift must specify a high-stability crystal (e.g., ±10 ppm) or use the internal calibration register to adjust offset, though the latter only corrects known deviations and not fundamental frequency error.
How should PCB layout considerations affect the implementation of the DS1501WS+T&R in high-noise environments?
The DS1501WS+T&R’s parallel interface is susceptible to electromagnetic interference (EMI), especially at 7.5 mm width and 28-pin SOIC packaging. To minimize noise coupling, traces for D0–D7, CS#, WR#, and RD# should be routed with matched lengths (<5 mm difference) and kept away from switching power inductors or clock lines. Ground planes beneath the package and guard rings around analog signals reduce crosstalk. Additionally, decoupling capacitors (100 nF ceramic) must be placed within 5 mm of VCC pins to suppress transient dips during write bursts, which could corrupt NVSRAM contents or reset the watchdog timer prematurely.
Is the watchdog timer feature in the DS1501WS+T&R suitable for critical system resets in safety-relevant designs?
The DS1501WS+T&R includes a configurable watchdog timer that resets the host microcontroller if no valid pulse is received within a user-defined window (ranging from 1 second to 8.39 minutes). This feature provides basic fault detection but lacks certification for functional safety standards like IEC 61508. It assumes the host system can fail to respond, but cannot detect partial hangs or corrupted instruction streams. For safety-critical applications, an external watchdog with independent clock source and hardened reset circuitry is recommended alongside the DS1501WS+T&R for redundancy.
What trade-offs exist between using the square wave output versus polling the parallel interface for periodic tasks with the DS1501WS+T&R?
The DS1501WS+T&R offers a programmable square wave output (1 Hz to 32.768 kHz) that eliminates CPU overhead compared to reading registers every second. However, selecting a higher frequency reduces resolution and increases power consumption due to continuous toggling. At 1 Hz, the output draws minimal current but offers coarse timing; at 32.768 kHz, it consumes more energy and may interfere with sensitive analog circuits unless filtered. Firmware polling allows dynamic updates and precise event capture but adds latency. In low-power embedded systems, the square wave is preferred for wake-up scheduling, whereas real-time diagnostics benefit from direct register reads via the parallel bus.
How does the Y2K compliance of the DS1501WS+T&R influence date handling in legacy system migrations?
The DS1501WS+T&R implements full Y2K compliance by storing years in four-digit format (YY-MM-DD-dd), avoiding the ambiguity of two-digit years. This ensures correct interpretation of dates beyond 2000, including leap years and century transitions. When integrating into older codebases designed for 2-digit year assumptions, software must be updated to interpret stored values correctly—failure to do so results in miscalculations such as treating 2025 as 1925. The hardware itself handles all calendar logic internally, so migration effort lies primarily in application-layer parsing rather than peripheral redesign.
What precautions are necessary when initializing or writing to the NVSRAM portion of the DS1501WS+T&R?
The 256-byte NVSRAM block shares address space with RTC registers, requiring careful initialization sequences to avoid accidental time corruption. Before writing data, the firmware must disable timekeeping interrupts and ensure no pending alarm flags are set. Write cycles must complete within the maximum tW (write pulse width) of 500 ns, and the chip select (CS#) must remain asserted throughout. After writing, a dummy read cycle is recommended to confirm successful transfer. Failure to follow these steps has led to observed cases where partial writes resulted in inconsistent time values alongside valid NVSRAM content.
Can the DS1501WS+T&R coexist with other peripherals on the same parallel bus without causing bus contention?
The DS1501WS+T&R uses standard active-low chip select (CS#), read (RD#), and write (WR#) signals compatible with most microcontrollers. However, multiple devices sharing the same address space require unique CS# lines to prevent overlapping asserts. If multiple slaves use open-drain outputs or tri-state buffers, additional pull-up resistors may be needed to meet rise time requirements (<1 µs). In systems with flash memory or EPROM also on the bus, careful timing analysis is required to avoid race conditions during simultaneous access attempts, particularly when the DS1501WS+T&R drives data lines while another device is outputting.
What role does the moisture sensitivity level (MSL) classification play in storage and handling of the DS1501WS+T&R?
Classified as MSL 1, the DS1501WS+T&R is exempt from moisture-induced damage concerns during normal handling and storage. This means it can be exposed to ambient humidity levels without requiring bake-out procedures prior to reflow soldering, simplifying manufacturing logistics. However, prolonged exposure to condensation (e.g., in unconditioned warehouses) may still cause solder joint defects post-reflow. Best practice remains storing components in sealed antistatic bags with desiccant until immediate use, regardless of MSL rating.
How does the parallel interface bandwidth limit practical applications of the DS1501WS+T&R in high-throughput logging systems?
With an 8-bit parallel interface and maximum clock speed of 1 MHz, the DS1501WS+T&R supports theoretical throughput of ~1 MB/s, but real-world data transfers are constrained by firmware overhead. A typical 256-byte NVSRAM write takes approximately 250 µs, limiting sustained logging rates to under 1 KB/sec. For applications requiring faster data capture (e.g., sensor burst sampling), buffering data in external RAM or using interrupt-driven DMA becomes essential. Alternatively, switching to an I²C or SPI-based RTC would yield significantly higher throughput, though at the cost of reduced integration density and added component count.
Are there any known errata or silicon revisions of the DS1501WS+T&R that affect reliability in field deployments?
Maxim Integrated has issued minor application notes addressing rare cases where the oscillator fails to start after deep discharge below 1.5V, particularly when using low-capacity backup batteries (<150 mAh). Although not formally listed as errata, field reports indicate improved robustness when pairing the DS1501WS+T&R with a backup supercapacitor or larger CR2032 cell. Additionally, some early production lots exhibited increased leakage current (~6 mA vs. spec’d 4 mA) under 3.6V supply, potentially shortening backup duration. Users should consult the latest datasheet revision and contact manufacturer support for batch-specific guidance.
What is the significance of the HTSUS code 8542.39.0001 for procurement and import purposes involving the DS1501WS+T&R?
The Harmonized Tariff Schedule of the United States (HTSUS) code 8542.39.0001 classifies the DS1501WS+T&R as an integrated circuit under semiconductor device provisions, generally qualifying it for duty-free treatment under USMCA or GSP programs depending on origin. Accurate classification avoids customs delays and ensures compliance with export controls. Importers should verify country of manufacture, as some regions may attract different tariff rates under bilateral agreements, affecting total landed cost in large-volume procurement scenarios.
How does the RoHS 3 compliance status of the DS1501WS+T&R impact material selection for high-reliability aerospace or medical applications?
RoHS 3 compliance confirms absence of restricted substances including lead, mercury, cadmium, hexavalent chromium, PBBs, and PBDEs, meeting EU environmental directives. While necessary for commercial distribution, it does not guarantee suitability for extreme environments. High-reliability sectors often require additional screening, conformal coating compatibility verification, and traceability to military or ISO-certified processes. The DS1501WS+T&R meets RoHS 3 but must undergo further qualification if deployed in avionics or implantable devices subject to stricter material regulations beyond base compliance.

Parts with Similar Specifications

The three parts on the right have similar specifications to Analog Devices Inc./Maxim Integrated DS1501WS+T&R

Product Attribute DS1501WSN+T&R DS1501WEN+T&R DS1501WSN/T&R DS1501WS/T&R
Part Number DS1501WSN+T&R DS1501WEN+T&R DS1501WSN/T&R DS1501WS/T&R
Manufacturer Analog Devices Inc./Maxim Integrated Analog Devices Inc./Maxim Integrated Analog Devices Inc./Maxim Integrated Analog Devices Inc./Maxim Integrated
Voltage - Supply, Battery - - - -
Package / Case - 196-LFBGA 16-DIP (0.300', 7.62mm) 64-VFQFN Exposed Pad
Voltage - Supply - - - -
Memory Size - - - -
Operating Temperature - -40°C ~ 85°C 0°C ~ 70°C -40°C ~ 85°C
Base Product Number - DAC34H84 MAX500 ADS62P42
Package - Tape & Reel (TR) Tube Tape & Reel (TR)
Date Format - - - -
Current - Timekeeping (Max) - - - -
Type - - - -
Series - - - -
Supplier Device Package - 196-NFBGA (12x12) 16-PDIP 64-VQFN (9x9)
Interface - - - -
Time Format - - - -
Features - - - Simultaneous Sampling
Mounting Type - Surface Mount Through Hole Surface Mount

DS1501WS+T&R Datasheet PDF

Download DS1501WS+T&R pdf datasheets and Analog Devices Inc./Maxim Integrated documentation for DS1501WS+T&R - Analog Devices Inc./Maxim Integrated.

Datasheets
DS1501, 11.pdf
Application Notes
Crystal Considerations with Maxim Real-Time Clocks.pdf Selecting a Backup Source for Real-Time Clocks.pdf
Environmental Information
Maxim Integrated REACH.pdf Maxim Integrated RoHS Cert.pdf

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Customer Reviews

Evaluation: 10 Articles

  • Nath***rooks
    Jun 11, 2026

    Installed this power component in a converter board. Output remained stable under different load conditions and thermal performance was better than expected.

  • Dani***alkerTech
    Jun 1, 2026

    Product works, but setup took more effort than expected. Once configured the MCU ran reliably, although documentation support felt older compared with newer platforms. Fine for maintenance projects.

  • Yuki***aka88
    May 26, 2026

    信号通信プロジェクトでこのRS-485トランシーバーを使用しました。設置は簡単で、長距離ケーブルでも通信は安定していました。消費電力も、以前使用していたものより低くなっています。

  • Stev***aker
    May 20, 2026

    Solid diode for power rectification. Works well in switching circuits.

  • Bran***Lewis
    May 11, 2026

    Compact FPGA with good performance. Suitable for basic signal processing tasks.

  • Oliv***arris
    May 7, 2026

    Reliable I/O expander. Works well in embedded control applications.

  • Jess***Jones
    Apr 17, 2026

    It offers good value for the price, and the specifications match the description. I’ve been using it for two days with no issues, and I’ll definitely buy it again if I need it in the future.

  • Mich***Smith
    Apr 17, 2026

    Shipping was on time, the component pins are neatly aligned, and I tested 10 of them with a multimeter—all readings were within the specified range. Highly recommended.

  • Aman***arris
    Apr 3, 2026

    It was great—the entire process, from placing the order to receiving the package, went very smoothly. The components were consistent, the price was fair, and I had a very pleasant shopping experience.

  • Mike***nch
    Apr 3, 2026

    Better than expected! The resistance and capacitance readings were spot-on, and it passed the test on the first try. The service was reliable, and the packaging was thoughtful—I highly recommend it.

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DS1501WS+T&R Image

DS1501WS+T&R

Analog Devices Inc./Maxim Integrated
32D-DS1501WS+T&R

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