RS5C338A-E2-F

Real Time Clock Overview

The RS5C338A-E2-F is a CMOS real-time clock IC featuring a 3-wire serial interface (CE, SCLK, SIO) and integrated voltage monitoring. It operates within a timekeeping supply voltage range of 1.45 V to 5.5 V, with a typical standby current of 0.35 µA at 3 V. The device provides BCD-format time and calendar counters, two alarm circuits, and selectable periodic interrupts. It includes an oscillation halt sensing circuit, high-precision frequency adjustment, and a 32-kHz clock output. Packaged in a compact 10-pin SSOP, the component supports automatic leap year identification up to 2099.

Real Time Clock Feature Summary

• 3-Wire Serial Interface: Connects via CE, SCLK, and SIO lines with a maximum clock frequency of 2 MHz.
• Voltage Monitoring: Includes a supply voltage monitoring circuit with selectable thresholds of 2.1 V or 1.6 V.
• Oscillation Adjustment: Built-in capacitors and correction circuit allow precision adjustments up to ±189 ppm.
• Alarm & Interrupts: Features Alarm_W and Alarm_D registers with periodic interrupt options ranging from 0.5 seconds to monthly.

Real Time Clock Applications

• Communication devices such as multi-function phones and portable units
• OA devices including fax machines and portable faxes
• Computer peripherals like PDAs and portable word-processors
• AV components such as digital cameras and remote controllers
• Home appliances including rice cookers and electric ovens

Real Time Clock Procurement Notes

The RS5C338A series is officially discontinued by Nisshinbo Micro Devices. Production has ceased, and the component is no longer available for new orders. Designers must verify end-of-life status before finalizing any hardware specifications. Replacement strategies should prioritize compatible successor models or alternative RTC solutions that meet the required interface and voltage specifications.

Real Time Clock Selection Notes

Select this component only if legacy compatibility is strictly required, as it is discontinued. Ensure the design accommodates the 10-pin SSOP package dimensions (6.4 × 3.5 mm). Verify that the system CPU supports the 3-wire serial protocol. Check that the operating voltage range (1.45 V to 5.5 V) aligns with the target application's power supply constraints.

Real Time Clock Part Context

The RS5C338A belongs to the R×5C338A series of real-time clocks manufactured by Nisshinbo Micro Devices (formerly Ricoh). The suffix 'E2' denotes the specific taping type for reel packaging. This series was designed for low-power applications requiring precise timekeeping and voltage supervision without complex I2C or SPI interfaces.

Real Time Clock Replacement Considerations

No direct public substitute part numbers are confirmed for this discontinued model. Engineers should evaluate other 3-wire serial RTCs or migrate to I2C/SPI-based alternatives from manufacturers such as Maxim Integrated or STMicroelectronics.

Real Time Clock FAQ

How does the oscillation halt sensing function work?

The XSTP bit in Control Register 2 is set to 1 when a halt in crystal oscillation is detected, such as during power-on from 0 volts or a supply voltage drop. This bit holds its state to indicate invalid data until manually reset to 0.

What are the selectable periodic interrupt frequencies?

The device offers five selectable frequencies: 2 Hz (0.5 seconds), 1 Hz (1 second), 1/60 Hz (1 minute), 1/3600 Hz (1 hour), and once per month.

Can the 32-kHz clock output be disabled?

Yes, the 32KOUT pin output can be disabled by setting both CLEN1 and CLEN2 bits to 1 or by pulling the CLKC pin low. It requires manipulation of two different registers to prevent accidental disabling.