When you’re designing a battery-operated portable system like security panels, or automatic locks, each and every inch on the board is important, each and every second of operation is important, and (last but not the least) each and every penny you pay for the system is important. These systems usually contain security codes retained by clocks, which can either be powered by the main power supply (main battery), or by the backup supply (backup battery). Losing the supply means losing the codes from the system, causing a security threat.
To avoid these threats, there is a lot of pressure on enhancing the performance and battery life of a system it. There is always a way to replace the main battery from the system but these small, tiny backup batteries can sometimes be very expensive to replace due to expensive labor costs. These batteries are used to keep the time and calendar running. Generally, as a system designer, you would want to keep your system running for as long as possible. To accomplish this, you have to either use a very fast-charging low-leakage and efficient solution, or use a RTC (real time clock) source. Both of these solutions can be very expensive and size inefficient when placed on a board discretely.
A smarter way to achieve a solution to this problem is a PMIC (Power Management Integrated Circuit), which integrates a small backup battery charger that can charge the backup batteries when the system is running and also power the RTC when the main batteries are taken off of the system. Figure 1 maps out an example of this.
Figure 1: RTC features in a PMIC
You can then maintain the RTC supply as long as the input voltage is a high enough set threshold in the PMIC. Below the set voltage threshold, the digital core of the device is set under reset by an internal signal power-on reset (POR), which clears all of the device contents.
Charging and discharging the battery with a fast charger is an ideal solution but there is an impact on the physical life of the battery when using this solution. PMICs not only provide you a quick charging solution but also an even better approach by integrating the RTC in the die. Due to the logic used for these clocks, the RTCs on the PMIC die are much lower in power consumption from using it discretely. The RTC in the PMIC consumes almost 1/250th less power than other implementations, which helps elongate system operation life. Power consumption for the PMIC RTC is usually 14uW as compared to 3.6mW when implemented externally. Also, it saves you the package cost of the device you pay when using it discreetly on the board.