When designing for human interface, programmable logic controller, thermostat or any battery powered applications, extending shelf life and improving standby time are big challenges. These challenges become even trickier when the end equipment sits idle for years on a shelf before it gets sold to end customers. The clocks in the devices still need to run to ensure the equipment wakes up at the right time.
Several options exist to improve the standby time for these applications – even up to 5 years. Normally to improve standby time, you might increase the battery size, which would make the system bulkier, or shut down the functions on the board to reduce the power consumption. The ideal situation is to improve system standby time while keeping the same battery chemistry and capacity.
Traditionally, the power circuit for a real-time clock (RTC) includes the 2 diodes, a low-dropout regulator (LDO) to power the RTC functions on the processors, and the diode switches between the main battery and backup battery (whichever is higher) to power the RTC. The total power loss in a circuit following this approach is about 63µW as shown in Figure 1. 80% of the total power loss occurs in the 2 LDO circuits. To compensate for the power loss from these 2 LDOs, you would need an 850mAh battery to improve system standby power.
With the TPS65218 integrated power-management solution, a 5-year shelf-life duration is possible with a battery as low as 300mAh for human interface or power line communication applications. The TPS65218 incorporates highly-efficient, dual low Iq DC/DC converters with an integrated power path that allows you to remove the external diodes from the board to decrease power loss. The highly efficient micropower converters cut power loss by almost 70%, as shown in Figure 2. The overall leakage of the LDO diodes can be replaced by the ultra-low leakage of the power-management integrated circuit (PMIC). The TPS65218 enables you choose a low capacity and cheaper coin-cell battery, which reduces overall system cost significantly. And the TPS65218 PMIC enables a 300mAh battery to keep the system on standby for 5 years.
Are you designing applications that can benefit from a 5-year standby time?