DS1338U-18

Real Time Clock Overview

The DS1338U-18 is a low-power serial real-time clock (RTC) and calendar integrated circuit manufactured by Analog Devices Inc./Maxim Integrated. It features full binary-coded decimal (BCD) timekeeping with leap-year compensation valid up to the year 2100, alongside 56 bytes of battery-backed NV SRAM. The device communicates via an I²C interface and includes a built-in power-fail detection circuit that automatically switches to a backup supply to maintain operation. Key electrical parameters include a primary supply voltage range of 1.71V to 5.5V, a battery supply range of 1.3V to 3.7V, and a maximum standby current of 100µA at 1.89V. It operates within an industrial temperature range of -40°C to +85°C.

Real Time Clock Feature Summary

• Full BCD clock/calendar with automatic month-end adjustments and leap-year compensation valid through 2100.
• Integrated power-fail detect and switch circuitry for seamless transition between VCC and VBAT supplies.
• Programmable square-wave output signal available at frequencies of 1Hz, 4kHz, 8kHz, or 32kHz.
• 56-byte battery-backed general-purpose RAM supporting unlimited write cycles.

Real Time Clock Applications

• Handheld devices such as GPS units and POS terminals.
• Consumer electronics including set-top boxes, digital recorders, and network appliances.
• Office equipment like fax machines, printers, and copiers.
• Medical devices such as glucometers and medicine dispensers.
• Telecommunications infrastructure including routers, switches, and servers.

Real Time Clock Procurement Notes

Verify the specific package variant when ordering, as the DS1338U-18 designation corresponds to the 8-pin µSOP package. Confirm RoHS compliance status, noting that suffixes like '+' indicate lead-free/RoHS-compliant devices while '#' denotes RoHS compliance potentially including exempt lead. Ensure the required operating voltage matches the -18 suffix specification (1.71V–5.5V) rather than other variants in the family.

Real Time Clock Selection Notes

Select the DS1338U-18 when an 8-pin surface-mount footprint is required for space-constrained designs. This variant supports both standard mode (100kHz) and fast mode (400kHz) I²C communication. Consider the external crystal requirements; unlike the DS1338C series, this model requires an external 32.768kHz crystal with a 12.5pF load capacitance connected to pins X1 and X2.

Real Time Clock Part Context

The DS1338U-18 belongs to the broader DS1338 family of serial RTCs from Maxim Integrated (now Analog Devices). While the core functionality remains consistent across the family, the 'U' suffix specifically identifies the compact 8-pin µSOP package option. Other family members include the SOIC packages (DS1338Z) and the integrated crystal version (DS1338C), offering designers flexibility in board layout and component count.

Real Time Clock Replacement Considerations

Direct pin-compatible replacements within the same package type include the DS1338U-3+ and DS1338U-33+, which share the 8-pin µSOP form factor but operate at different nominal supply voltages (3.0V and 3.3V respectively). Verify that the system's power rails align with the replacement part's recommended operating conditions before substitution.