Maintaining the resistor divider ratio during start-up

摘要

Circuits and methods to maintain a resistive voltage divider ratio during start-up of an electronic circuit comprising a feed-forward capacitor across a feedback resistor using a dynamic start-up circuit are disclosed as e.g. a LDO or an amplifier. In a preferred embodiment of the disclosure is applied to an LDO. Modification of the resistive voltage divider ratio caused by the feed-forward capacitor during start-up is prevented while the voltage level of a voltage access point of the voltage divider on the feed-forward capacitor is maintained. A start-up circuit comprises a start-up capacitor and a start-up comparator.

主权项

1. A method to maintain a resistive voltage divider ratio during start-up of any electronic circuit comprising a feed-forward capacitor across a second feedback resistor of a resistive voltage divider using a dynamic start-up circuit, comprising the following steps:
(1) providing the electronic circuit comprising the feed-forward capacitor across the second feedback resistor of the resistive voltage divider, a differential amplifier, and the dynamic start-up circuit comprising a start-up comparator and a start-up capacitor across a first feedback resistor of the resistive voltage divider and switching means; (2) avoiding modification of the resistive voltage divider ratio caused by the feed-forward capacitor during start-up phase by the dynamic start-up circuit, wherein the start-up capacitor is connected to a voltage mid-point of the resistive voltage divider during start-up phase only; (3) monitoring an output voltage of the electronic circuit and finish start-up-phase when a desired output voltage of the electronic circuit is reached, wherein the start-up comparator detects if the desired output voltage of the electronic circuit is reached by comparing a voltage representing the output voltage of the electronic circuit with a reference voltage and once both voltages are the same the start-up phase is finished; and (4) processing normal operation after start-up phase is finished wherein the start-up comparator disconnects via the switching means the start-up capacitor from the voltage mid-point of the resistive voltage divider when the start-up phase is finished.