DS1338U-33+ - I²C RTC with 56B NV RAM | Analog Devices
MPN: DS1338U-33+ ✓ ActiveDS1338U-33+ Overview
A real-time clock is an integrated circuit that maintains time independently of a system processor. The RTC category sits within clock and timing ICs and broader semiconductor timing systems. Unlike a software timer, the DS1338U-33+ can preserve calendar time when the main supply is removed and the device is connected to a backup source, making it useful for systems requiring time stamps, event logging, or scheduling after power restoration.
The DS1338U-33+ combines a full BCD clock/calendar with 56 bytes of NV SRAM in one package. Its serial address and data path uses the I²C interface, reducing the number of microcontroller connections compared with a parallel calendar device. The manufacturer describes automatic month-end adjustment for months containing fewer than 31 days, which reduces firmware work when validating date rollover behavior.
The integrated SRAM gives the host controller space for small quantities of persistent data without adding a separate memory IC. Applications can store configuration bytes, counters, alarms, or system state alongside the calendar. Because the available source data does not state the exact endurance, retention time, current consumption, oscillator accuracy, or I²C address, those values should be confirmed in the manufacturer datasheet before final qualification.
Typical uses include industrial controllers, data loggers, metering equipment, embedded instruments, and access-control or security systems that need a persistent timestamp. The I²C interface is particularly convenient for microcontrollers and system processors that already use a two-wire bus. Designers should account for I²C pull-up resistors, address selection, backup-source isolation, and startup behavior when the main supply returns.
The principal design consideration is preserving the correct time across power loss. Follow the manufacturer backup-battery guidance, use the specified decoupling and pull-up networks, and avoid loading the backup source when the main supply is active. Verify the exact package variant and pin mapping against the ordering code because the supplied distributor records reference both 8-TSSOP and 8-MSOP forms.
This product record combines current distributor availability, manufacturer functional details, package information, and verified cross-reference results. It also distinguishes documented drop-in candidates from merely similar RTC devices, helping engineers avoid assuming that equivalent timekeeping functions guarantee identical pin compatibility, memory capacity, or package geometry.
Drop-in alternatives for DS1338U-33+ — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with DS1338U-33+ (same form factor and footprint) — differing in Calendar Fields.
DS1338U-3+
✅ Drop-InContact for price
View Datasheet →DS1339U-2+
✅ Drop-In📋 Reference alternative (not in catalog)
DS1338U-33+ Specifications
| Device Type | Serial real-time clock and calendar with NV SRAM |
| Timekeeping Format | Full binary-coded decimal (BCD) |
| Calendar Fields | Seconds, minutes, hours, day, date, month, and year |
| Serial Interface | I²C, 2-wire serial |
| Integrated NV SRAM | 56 bytes |
| Minimum Supply Voltage | 3 V |
| Maximum Supply Voltage | 5.5 V |
| Nominal Supply Voltage | 3.3 V |
| Package Options Referenced | 8-TSSOP and 8-MSOP, 0.118 inch and 3.00 mm width |
| Number of Pins | 8 pins |
| Mounting Type | Surface-mount technology (SMT) |
| Terminal Form | Gull wing |
| Temperature Grade | Industrial |
| Minimum Operating Temperature | -40 °C |
| Month-End Adjustment | Automatic for months with fewer than 31 days |
DS1338U-33+ 8-tssop and 8-msop, 0.118 inch and 3.00 mm width Pin Configuration Guide
Pin configuration for DS1338U-33+ (8-tssop and 8-msop, 0.118 inch and 3.00 mm width package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for DS1338U-33+.
Refer to the datasheet for full pin configuration.
Typical Applications
DS1338U-33+ is suitable for 6 applications: Industrial Data Loggers, Battery-Backed Embedded Instruments, Metering and Utility Data Collection, Access-Control and Security Systems, Programmable Controllers and Automation, Networked Monitoring Equipment.
Industrial Data Loggers
The DS1338U-33+ fits industrial data loggers that must attach reliable timestamps to sampled process or environmental data. Its I²C interface shares two signal lines with the host microcontroller, while the full BCD clock/calendar records seconds through year and automatically handles month-end rollover for shorter months. The integrated 56-byte NV SRAM can hold limited counters, alarms, or operating-state information without a separate memory component. Because the verified source does not state oscillator accuracy, designers should qualify it against the product's timestamping interval, enclosure temperature, and supply-noise environment before deployment.
Recommended
Battery-Backed Embedded Instruments
The DS1338U-33+ is appropriate for embedded instruments that need to retain wall-clock time through a mains interruption. Its 3 V to 5.5 V operating range supports 3.3 V systems, and its 56-byte NV SRAM provides limited persistent storage alongside the calendar. A host controller can read the time over I²C without consuming a dedicated parallel interface. Integration requires care around the backup source, decoupling, and I²C pull-ups, while the exact backup current and oscillator behavior must be confirmed from the complete manufacturer datasheet.
Recommended
Metering and Utility Data Collection
The DS1338U-33+ supports metering equipment that must associate consumption records with a calendar timestamp. Its full BCD calendar includes seconds, minutes, hours, day, date, month, and year, enabling scheduled reads and event logging through an I²C-connected controller. Automatic end-of-month adjustment reduces date-boundary errors without relying entirely on host firmware. The 56-byte NV SRAM can retain a small configuration record, although storage-intensive metering histories should remain in external nonvolatile memory. Validate time accuracy over the required temperature and aging interval using manufacturer documentation.
Recommended
Access-Control and Security Systems
The DS1338U-33+ can provide timekeeping for access-control terminals, alarm panels, and security recorders where event ordering depends on a trusted wall clock. The I²C interface limits wiring to a host controller already attached to a two-wire bus, and the RTC continues maintaining calendar information when the primary system is unpowered. The 56-byte NV RAM is useful for small state variables but is not intended as a general audit-log buffer. Backup-source isolation, power-fail behavior, and security requirements should be reviewed against the manufacturer documentation before installation.
Recommended
Programmable Controllers and Automation
The DS1338U-33+ is useful in programmable automation controllers that need time-based scheduling, run-hour tracking, and periodic event logging. A host processor can access calendar and alarm data through I²C, while the on-chip 56-byte NV SRAM stores compact operating parameters across resets. Month-end adjustment is handled automatically, but leap-year and application-specific calendar rules should still be tested in system firmware. The device's industrial-grade classification makes it a candidate for factory equipment, provided the complete operating-temperature range and timing accuracy are confirmed during design qualification.
Recommended
Networked Monitoring Equipment
The DS1338U-33+ can add a local, battery-backed time reference to monitoring equipment that must continue recording events during a network or mains outage. Its I²C interface is compatible with a host processor's two-wire peripheral bus, and the BCD calendar provides the standard date and time fields expected by many logging systems. The 56-byte NV RAM provides limited persistent state but should not be treated as a large event buffer. Engineers should account for I²C bus contention, pull-up selection, backup-source charging, and recovery behavior when the primary supply returns.
Recommended
Recommended Products Summary
Engineering reference data for DS1338U-33+ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | DS1338U-3+ | DS1339U-2+ |
|---|---|---|---|
| Package | 8-TSSOP / 8-MSOP | 8-TSSOP / 8-MSOP | 8-TSSOP / 8-MSOP |
| Brand | Analog Devices | Analog Devices | Analog Devices |
| Device Type | Serial real-time clock with NV SRAM | DS1338U family RTC | DS1339 family RTC |
| Serial Interface | I²C, 2-wire serial | I²C | I²C |
| Nominal Configuration | 3.3 V | 3.0 V | 2.0 V |
| Number of Pins | 8 pins | 8 pins | 8 pins |
Key Differentiators
- Clock/calendar and persistent storage in one component (vs DS1339U-2+)
- Directly verified family comparison (vs DS1338U-3+)
- Three-volt compatible operation for embedded systems (vs DS1339U-2+)
- Established multi-distributor channel availability (vs DS1339U-2+)
Design Notes
Design the backup-supply path around the manufacturer's DS1338U guidance. The verified data confirms a 3 V to 5.5 V operating range and identifies battery-backed timekeeping as a core use case, but it does not provide the backup-source charging topology or leakage limits. Do not infer whether a primary rail may connect directly to the backup input. Confirm the exact circuit in the manufacturer datasheet and validate it for both backup-current and main-supply-present conditions.
Place the I²C pull-up network close to the bus master and route the SDA and SCL traces as a compact, matched pair away from noisy power-converter nodes. The DS1338U-33+ has only 56 bytes of NV SRAM, so decoupling and layout should be optimized for deterministic data transfer rather than high-bandwidth operation. Use the package-specific land pattern and pin numbering from the manufacturer datasheet because the supplied distributor excerpts reference both TSSOP and MSOP forms.
Do not treat a similar RTC as a drop-in replacement merely because it also uses I²C and retains 56 bytes of memory. The suffix can affect the configured supply or backup behavior, while package body dimensions and exposed-pad details may differ. The verified cross-reference list names MCP7940M, MCP7940T, and PCF8523 as functionally similar, but it explicitly warns that voltage, interface, and package compatibility must be checked. Compare the complete pin tables and footprint drawings before substitution.
The I²C bus should remain within the voltage limits and rise-time requirements specified by the manufacturer. A pull-up value that is too high can create slow edges, while a value that is too low may exceed the sink-current capability of the DS1338U-33+ or the host controller. Account for bus capacitance, pull-up tolerance, leakage from connected devices, and the maximum number of nodes on the bus. The supplied excerpts do not specify the device address or electrical timing, so those values must come from the complete datasheet.
Compliance Information
The supplied verified excerpts describe the DS1338U-33+ as an industrial-grade RTC but do not provide explicit RoHS, REACH, lead-free, halogen-free, conflict-minerals, or automotive-qualification statements. Compliance fields are therefore left unknown rather than inferred.
