https://www.pcbway.com/project/sharepro ... 216ed.html
It is based on AN_SY8088 DC-DC voltage regulator IC. It is a high-frequency synchronous DC to DC step-down voltage regulator with an operating current of about 1A and an input voltage of about 2.5 to 5V. It is good for powering up the ESP8266 which requires 3V3 DC.