RTC 22 Click

How does it work?

RTC 22 Click is based on the AM1805AQ, an ultra-low-power real-time clock with integrated power management from Ambiq. Using Ambiq’s proprietary SPOT® (Subthreshold Power Optimized Technology) CMOS platform, this RTC sets a new industry standard with power consumption as low as 14nA, making it an ideal solution for power-sensitive applications. The AM1805AQ incorporates on-chip oscillators to ensure minimal power usage while providing full RTC functionality, including battery backup, programmable timers, counters, and alarms, along with an I2C interface for communication with a host MCU. Its integrated power switch and intelligent system sleep manager enable precise control over power states, allowing the RTC to be a supervisory component in MCU-based systems such as medical devices, utility meters, data loggers, household appliances, consumer electronics, and communication equipment.

The AM1805AQ’s functionality is divided into baseline timekeeping, advanced timekeeping, and power management. Baseline timekeeping uses a 32.768kHz crystal oscillator, offering maximum frequency accuracy with an ultra-low current draw of just 55nA. Its digital calibration algorithm ensures frequency tuning accuracy down to 2ppm at specific temperatures. Advanced timekeeping introduces additional oscillation modes, including an RC oscillator and an auto-calibration mode, along with a finite state machine that manages host MCU transitions between active and low-power states. The integrated power switch, with an impedance of approximately 1Ω, can cut off ground current to the host MCU, reducing sleep current to below 1nA, making RTC 22 Click an essential component for any low-power embedded system.

RTC 22 Click is powered from the 3.3V mikroBUS™ power rail but also supports standalone operation, thanks to the PWY0150S micro-energy storage device from ITEN. This highly integrated, high-power-density battery delivers up to 20mA of current with a capacity of 150µAh in a compact SMD QFN package. Designed for high performance, it supports fast charging and can endure up to 1000 cycles at 100% depth of discharge (DoD). PWY0150S’s contribution to the design ensures reliable and efficient energy storage, enabling RTC 22 Click to maintain functionality even in low-power scenarios.

The battery is recharged by the onboard XC6240 series charging IC for rechargeable batteries, providing a stable 2.7V charging voltage after battery depletion. Battery power can be enabled via the VBAT switch by toggling it from OFF to ON. Transitioning to standalone operation allows for significant power savings by cutting specific traces on the back of the board, which disables the lower part of the board below the RESET button, including the power indicator and ClickID circuitry. In this low-power mode, the timer interrupt signal can be used on the IRQ pin by connecting the right-side LP CUT trace on the back of the board, whereas in normal operation, this pin is reserved for ClickID communication.

This Click board™ communicates with the host MCU via an I2C interface, supporting clock frequencies up to 400kHz to ensure fast and reliable data exchange. Alongside the standard I2C pins, the board includes an INT pin, an open-drain interrupt output, that signals when the RTC is ready to be accessed through the serial interface. Additionally, the WDI pin serves as a watchdog timer reset signal, safeguarding against system failures by resetting the host MCU if it becomes unresponsive, thus ensuring continuous operation. This pin can also function as an external interrupt input, offering further flexibility for triggering specific events within the system.

RTC 22 Click also features a group of unsoldered pins that provide additional functionality and flexibility. On the left side of the board, the RSTO pin serves as an open-drain reset output signal from the main AM1805AQ IC, used to reset the host MCU or other connected devices when triggered by internal RTC events, ensuring proper system initialization and recovery. Alongside it, the EXTRST pin functions as an external reset input, allowing the host MCU or external sources to reset the RTC itself when necessary. This same reset functionality is also accessible via the onboard RESET button, offering a manual alternative for triggering a system reset.

On the right side, three unsoldered pins offer further capabilities: PSW acts as a power switch output for controlling external devices (also available as PSW pin on mikroBUS™ socket), turning their power supply ON or OFF; CLK provides a square-wave clock output that can serve as a precise timing reference for the host MCU or other peripherals; and EXTI functions as an external interrupt input, allowing external signals to trigger interrupts within the RTC, facilitating event-driven operations and synchronized timing in complex embedded systems.

This Click board™ can be operated only with a 3.3V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. It also comes equipped with a library containing functions and example code that can be used as a reference for further development.

Specifications

Pinout diagram

This table shows how the pinout on RTC 22 Click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
Power Switch Output	PSW	1	AN	PWM	16	WDI	Watchdog Timer Input
ID SEL	RST	2	RST	INT	15	INT	Interrupt
Timer Interrupt / ID COMM	IRQ	3	CS	RX	14	NC
	NC	4	SCK	TX	13	NC
	NC	5	MISO	SCL	12	SCL	I2C Clock
	NC	6	MOSI	SDA	11	SDA	I2C Data
Power Supply	3.3V	7	3.3V	5V	10	NC
Ground	GND	8	GND	GND	9	GND	Ground

Onboard settings and indicators

RTC 22 Click electrical specifications

Software Support

RTC 22 Click demo application is developed using the NECTO Studio, ensuring compatibility with mikroSDK's open-source libraries and tools. Designed for plug-and-play implementation and testing, the demo is fully compatible with all development, starter, and mikromedia boards featuring a mikroBUS™ socket.

Example Description

This example demonstrates the use of RTC 22 Click board by reading and displaying the time and date values.

Key Functions

• rtc22_cfg_setup Config Object Initialization function.
• rtc22_init Initialization function.
• rtc22_set_time This function sets the starting time values - second 100th, second, minute and hour.
• rtc22_read_time This function reads the current time values - second 100th, second, minute and hour.
• rtc22_set_date This function sets the starting date values - day of week, day, month and year.

Application Init

Initializes the driver, checks the communication, and sets the starting time and date.

Application Task

Reads and displays on the USB UART the current time and date values once per second.

Application Output

This Click board can be interfaced and monitored in two ways:

• Application Output - Use the "Application Output" window in Debug mode for real-time data monitoring. Set it up properly by following this tutorial.
• UART Terminal - Monitor data via the UART Terminal using a USB to UART converter. For detailed instructions, check out this tutorial.

Additional Notes and Information

The complete application code and a ready-to-use project are available through the NECTO Studio Package Manager for direct installation in the NECTO Studio. The application code can also be found on the MIKROE GitHub account.