Abstract

Today smart watches are often designed with the ability to measure blood oxygen and monitor heartbeat. The application works by means of an LED that emits light onto the wrist, while the photodiode on the other side receives the reflected light, comparing the difference between the emitted light and the received light to calculate the oxygen level. Low-frequency blinking of LEDs, is challenging low-power supply designs. Especially in the moment when the LEDs light up, the load current suddenly ramps up, the output voltage to fluctuate as a result. The shorter settling time is, the shorter LED illumination time is, as a result, the more energy consumption of a portable device such as the smart bracelet is saved. In this way, the settling time of the output voltage is of the importance. Therefore, the transient performance is often an important indicator in examining power devices in smart watch.

This application note proposes a power supply solution for the TPS61299 boost converter with fast transient performance. Compared to common power solutions, smart watch with TPS61299 can extend the standby time about one day, about 6.67%.