The trigger event always needs to be powered on so the event can respond on time. PIR is mostly applied in battery powered camera to detect if there is a human approaching. At times, PIR is not suitable for some location that is easily exposed to sunlight due to causing several false alarms to wake up the entire system. A low-cost mmWave (IWRL6432) detector has no such concerns. The detector only detects movement through Doppler way and immunity temperature and light. Wi-Fi is not only the main transferring video stream, Wi-Fi also need receive remote command such as starting recording command. But power consumption of Wi-Fi connection is not very small, so there are some approaches to improve it, such as using TWT of Wi-Fi6, using Wi-Fi SOC which Intermittently working and sleep, using Sub-1GHz private protocol to connect a special remote station, something like this. TI Wi-Fi SOC CC3235 is specially designed for low power consumption which is just 4.5 uA in hibernate mode and 120 uA in deep sleep mode.

Figure 4-2 is a common power structure design. Some low voltage power rails are a little different because of using different ISP SOC.

Li battery output voltage changing is respective with temperature and discharging time as shown Figure 4-3. To achieve most energy from battery and get a stable voltage for sensing and RF performance, buckboost component is a good option.

Figure 4-2 Battery Output Voltage and Discharge Time vs Temperature

TPS631000 is TI's latest and low-cost buck-boost component. TPS631000 SOT package and very few external components reduce total design cost.

Figure 4-3 TPS631000 Efficiency

TPS631000 is specially optimized design for battery power supply to make its efficiency mostly over 90%, even over 95%. It has 8uA typical quiescent current and 2MHz switching frequency. All of these make it very suitable applied for battery power system to save energy in always working mode.

TPS7A20 is 300-mA low cost LDO with 7 uVrms noise, 6.5 uA quiescent current and 95dB/1KHz high PSRR LDO. These features make it ideal for always working to power sensor in low power consumption system. its shutdown current is less than 5nA under Li battery power input. so it can be also used in system which need to be shutdown.

Although Wi-Fi components is always powered by TPS631000, power consumption of Wi-Fi connection is relevant big. In most instance, Wi-Fi SOC is working in interval working mode. CC3235’s SDK can support easily configured entering in deep sleep or hibernate mode and automatically be woken up by RTC or GPIO or remote network request.

Generally, always working power rails are major source of energy consumption, need give more consideration about power efficiency, quiescent current no matter in power converter, PIR LDO, PIR circuit, mmWave power rail, or Wi-Fi working mode.