Wireless Sensor Network (WSN) is an important component of healthcare. The design of the power management unit for WSN poses significant challenges, as it not only needs to achieve good current efficiency but also requires high power supply rejection (PSR) and good load transient performance. This paper presents a low-dropout regulator (LDO) with low quiescent current and fast transient response to adequately meet the power supply requirements of WSN systems. To ensure system stability and reduce voltage spikes during load transients, an adaptive frequency compensation network is integrated into the circuit. Additionally, the LDO incorporates a level shifter that facilitates bi-directional transmission of voltage signals across different power systems. The proposed LDO is designed and simulated in a 180 nm BCD process. It operates under a wide input voltage range from 0.8V to 5.5V, supports maximum load currents of up to 500mA, and allows output voltages to vary from 0.8V to 3.6V by adjusting the feedback resistance. As a result of implementing the adaptive frequency compensation circuit, the overshoot and undershoot voltages at an output voltage of 1V are measured to be only 23mV and 5mV, respectively. Moreover, the LDO achieves a PSR of 83dB for bias voltage and 98dB for input voltage at 1kHz. The level shifter's highest working frequency can reach 26MHz under supply voltages (VCCA = 1.65V to 5.5V; VCCB = 5V), thereby enabling high-speed data transmission. Finally, the LDO consumes a quiescent current of 42μA while incorporating a bandgap reference circuit and other auxiliary circuits.