A low-power real-time clock (RTC) can maintain a device's time and date while the main processor sleeps. Its value depends on the complete system: standby current, time accuracy, backup supply, board area and software behavior. Choosing a low-current part alone does not guarantee longer battery life or a smaller product.
Timekeeping still requires power
An RTC does not keep running without an energy source. If the main supply is removed, continued timekeeping requires a suitable backup battery, capacitor or other powered backup domain. The circuit must support the required voltage range and power-source switching behavior.
As one example, Texas Instruments describes the BQ32000 as an RTC with battery backup and a trickle-charge function. This illustrates the need to consider backup power alongside the clock IC. It is not a recommendation that this device fits every mobile design; compare the actual current, voltage, package and accuracy requirements.
Calculate the contribution to battery life
Measure the product's active, sleep and standby loads. Include the RTC, backup path, pull-up resistors, regulator losses and other always-powered circuits. A reduction in RTC current matters most when it is significant relative to the rest of that power budget.
For an illustrative calculation, reducing an always-on load by 1 microampere saves 0.024 mAh per day, or approximately 8.76 mAh over 365 days. That is an arithmetic example, not a prediction for a particular RTC or battery. Actual operating life also depends on battery capacity, self-discharge, temperature and the device's duty cycle.
Selection checks for a mobile-device design
| Requirement | Questions to resolve |
|---|---|
| Time accuracy | How much drift is acceptable between synchronization events? What temperature and aging effects apply? |
| Power modes | What are the timekeeping currents at the actual main and backup voltages? Which conditions accompany typical and maximum values? |
| Backup supply | What retention duration is needed? Is the backup source compatible with any charging circuit? |
| Interface | Are logic levels, bus access and power-off behavior compatible with the processor? |
| Timing features | Does the application need alarms, interrupts, calibration or oscillator-failure detection? Verify support on the selected part. |
| Physical design | Include the IC, crystal if required, backup source and supporting components in the area and cost estimate. |
Separate local timekeeping from network synchronization
An RTC maintains local time; it does not by itself provide wireless connectivity or keep multiple devices synchronized. Firmware must set and validate time and, where needed, update it from a suitable external reference. The application should also define what happens after backup power is exhausted or the oscillator stops.
Validate before making product claims
- Measure complete-board current in each operating mode.
- Test main-power removal, backup operation and restoration.
- Check time drift over the intended temperature range.
- Verify firmware handling of invalid time, alarms and power transitions.
- Compare total BOM, assembly and validation costs with the existing design.
Use these results to support battery-life and cost claims. An RTC choice alone does not demonstrate regulatory compliance, environmental benefits or a longer overall device lifespan.
When requesting components, include the full part number, package, temperature grade and required quantity. Review the datasheet checks for sourcing before submitting a component enquiry.
