CC-CV method to control the startup current for LDO

摘要

Methods and circuits for linearly controlling a limited, constant current during startup of LDOs, amplifiers, or DC-to-DC converters independent of load capacitor size and controlling a clean transition without glitches from a constant current (CC) mode during startup to a constant voltage (CV) mode during normal operation (CC-CV method) are disclosed. The constant current control loop and the constant voltage control loop are implemented in such a way that at the end of startup the voltage loop has taken over control and the current loop is moved far away from its active transistor region, allowing a switch of modes to occur without any nasty transitions on the output.

主权项

1. A method for linearly controlling a limited, constant current during startup of a circuit of an electronic apparatus until an output voltage is close a target voltage of normal operation is reached independent of load capacitor size and a clean transition without glitches from a constant current (CC) mode during startup to a constant voltage (CV) mode during normal operation (CC-CV method), the method comprising the steps of:
(1) providing a circuit of an electronic apparatus comprising a load capacitor, a current sensing means, a current control loop, comprising a current control transistor to set and control the start-up current and to control a current limit during normal operation in order to keep the output current below a maximum limit, and a voltage control loop to control the output voltage during normal operation, wherein the voltage control loop comprises a voltage control transistor; (2) sensing and controlling linearly the startup current by the current control loop to get a constant, limited start-up current of the circuit during start-up phase until an output voltage of the circuit is close to a target value, wherein the current control transistor wherein the current control transistor operates in saturation mode during the startup phase; and (3) starting, when the output voltage of the circuit is close to the target value, to shift from constant startup current control mode to constant output voltage mode controlled by a voltage control loop and to shift to current limit control of normal operation by the current control loop by gradually shifting the current control transistor from saturation mode to linear mode and finally to triode mode achieving a seamless transition from constant current mode to constant voltage mode to occur without any glitches on the smoothing load capacitor.