A Cable-Drop Compensated LDO for Rechargeable Battery Powered Systems With Load Current Management in Two-Cable or Three-Cable Structures

This paper presents a low-dropout (LDO) regulator structure that is aimed at rechargeable battery powered systems where direct sensing of the load voltage is not available. The cable connecting the regulated output to the load may create a voltage drop and cause error to the load voltage. Conventional methods address this issue by increasing the LDO output voltage to compensate the cable voltage drop. The proposed architecture extends this idea by including a calibration block that updates the required compensation voltage to track the cable resistance shift due to cable length or temperature change. The measured cable-drop error was reduced from 2.4% to ~0.1% by iterating the proposed calibration process three times. Under the condition of time-varying temperature, the measured calibration process effectively reduced the cable-drop error due to the temperature-coefficient of the cable resistance. The proposed system also includes a current management block, by which the priority is set between the load current and the battery charging current. This paper proposes two architectures, the two-cable and the three-cable structures, to implement both the cable-drop calibration and the current management functions. Other functions such as input under-voltage-lockout and output current-limiting are also included and have been verified by experiment.