RS5C372B-E2-F

Real Time Clock Overview

The RS5C372B-E2-F is a CMOS real-time clock IC featuring an I2C bus interface for serial data transmission. It operates within a supply voltage range of 2.0V to 6.0V, with a timekeeping voltage minimum of 1.45V. The device maintains low standby current, typically 0.5µA at 3V and 25°C. It includes BCD-coded counters for seconds, minutes, hours, day of the week, date, month, and year, supporting automatic leap year recognition until 2099. Key features include dual alarm systems, periodic interrupts, oscillation halt sensing, and a high-precision time trimming circuit. The component is housed in an 8-pin SSOP package.

Real Time Clock Feature Summary

• I2C Bus Interface: Supports standard mode (up to 100kHz) and fast mode (up to 400kHz) communication via SCL and SDA pins.
• Low Power Consumption: Standby current is typically 0.5µA at 3V/25°C and 1.0µA maximum at 3V/-40°C to +85°C.
• Dual Alarm & Interrupts: Features two alarm systems (Alarm_A, Alarm_B) and periodic interrupt outputs selectable by frequency or level mode.
• Time Trimming Circuit: Incorporates internal capacitance and a trimming function to adjust clock accuracy up to ±189ppm.

Real Time Clock Applications

• Communication devices such as multi-function phones, portable phones, PHS, and pagers
• Office automation equipment including fax machines and portable faxes
• Computers like desktop/mobile PCs, PDAs, and electronic notebooks
• Audio/Video components such as digital cameras, video cameras, and remote controllers
• Home appliances including rice cookers and electric ovens

Real Time Clock Procurement Notes

Verify the specific ordering suffix 'E2' corresponds to the taping type and 'F' indicates lead-free plating as defined in the selection guide. Confirm that the application design supports the 2.0V minimum VDD requirement for the RS5C372B variant, which differs from the RS5C372A's 1.7V minimum. Ensure pull-up resistors are appropriately sized for the desired I2C speed and voltage levels on the SCL and SDA lines.

Real Time Clock Selection Notes

Select the RS5C372B over the RS5C372A if a dedicated CMOS push-pull output pin (Pin 1, 32KOUT) is required for the 32.768kHz clock signal, rather than sharing it with an interrupt pin. Note that the RS5C372B requires a minimum VDD of 2.0V for standard I2C operation, whereas the RS5C372A supports down to 1.7V. Both variants share identical pinouts for power, I/O, and oscillator connections but differ in interrupt pin configuration and control register bit definitions.

Real Time Clock Part Context

The RS5C372B is part of the RS5C372 family of CMOS real-time clocks manufactured by Nisshinbo Micro Devices. It serves as a variant to the RS5C372A, primarily distinguished by its output pin configuration for the 32kHz clock and its slightly higher minimum operating voltage. The family is designed for compact, low-power applications requiring precise timekeeping and calendar functions via a simple 2-wire interface.

Real Time Clock Replacement Considerations

The RS5C372A is a functional alternative within the same package but requires verification of voltage compatibility (1.7V vs 2.0V min) and pin mapping differences for the 32kHz output and interrupt signals. Direct substitution requires adjusting firmware to account for different control register bits (SL1/SL2 usage) and hardware changes if the 32kHz output drive strength or pin location is critical.

Real Time Clock FAQ

What is the difference between the RS5C372A and RS5C372B regarding the 32kHz output?

The RS5C372B provides a dedicated CMOS push-pull output pin (Pin 1, 32KOUT) for the 32.768kHz clock. In contrast, the RS5C372A outputs the 32kHz clock on the INTRB pin, which is an Nch open-drain output shared with interrupt functions.

How does the time trimming circuit work in the RS5C372B?

The RS5C372B incorporates a high-precision time trimming circuit that adjusts the clock gain or loss based on CPU signals. It can correct discrepancies up to approximately ±189ppm (±194ppm with a 32.000kHz crystal) in steps of 3ppm, achieving an error of ±1.5ppm at 25°C after correction.

Can the RS5C372B operate in Fast Mode I2C?

Yes, the RS5C372B supports Fast Mode I2C operation with a maximum SCL clock frequency of 400kHz, provided the supply voltage (VDD) is at least 2.5V.