Maintaining the Resistor Divider Ratio During Start-Up
AssigneeDialog Semiconductor GmbH
InventorsAmbreesh Bhattad, Ludmil Nikolov, Marinus Wilhelmus Kruiskamp
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Abstract
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.
Claims15
A method to maintain a resistive voltage divider ratio during start-up of any electronic circuit comprising a feed-forward capacitor across a feedback resistor of a resistive voltage divider using a dynamic start-up circuit, comprising the following steps:
- (1) providing an electronic circuit comprising a feed-forward capacitor across a second feedback resistor of a resistive voltage divider, a differential amplifier, and a 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 resistive voltage divider ratio caused by feed-forward capacitor during start-up phase by the start-up circuit;
- (3) monitoring output voltage and finish start-up-phase when desired output voltage of the electronic circuit is reached;
- and
- (4) processing normal operation after start-up phase is finished wherein the start-up capacitor is separated from a mid-point of the voltage divider after end of start-up phase.
A circuit to maintain a resistive voltage divider ratio during start-up of any electronic circuit comprising a feed-forward capacitor across a second feedback resistor and a resistive voltage divider using a dynamic start-up circuit, comprising:
- a pass transistor connected between a VDD voltage and an output port of the circuit, wherein a gate of the pass transistor is connected to an output of an output port of a differential amplifier;
- said differential amplifier having two inputs wherein a first input is a reference voltage and the second input is a voltage representing the output voltage of the circuit;
- said feed-forward capacitor, wherein a first plate of the feed-forward capacitor is connected to the output port of the circuit and a second plate is connected to a voltage access point of the resistive voltage;
- said resistive voltage divider, being connected between the output port of the circuit and ground, comprising the second feedback resistor having a resistance R2, connected between the output port of the circuit and the voltage access point in-between the voltage divider having a fraction of the output voltage, and further comprising a first feedback resistor having a resistance R1, being connected between the voltage access point in between the voltage divider and ground;
- and
- a start-up circuit comprising:
- a start-up comparator configured to detect if the start-up phase is finished by being configured to compare the voltage representing the output voltage of the electronic circuit with the reference voltage wherein the start-up comparator is also configured to separate, via a first switching means, a start-up capacitor from the voltage access point of the resistive voltage divider when the start-up phase is finished;
- the start-up capacitor across the first feedback resistor of the resistive voltage divider, wherein the start-up capacitor is connected to the voltage access point of the resistive voltage divider during the start-up phase only;
- and
- said first switching means connected between the voltage access point of the voltage divider and the start-up capacitor.
The circuit of claim 23 wherein the start-up capacitor has a capacitance C=CFF×R2/R1, wherein CFF is the capacitance of the feed-forward capacitor, R1 is the resistance of the first resistor of the voltage divider and R2 is the resistance of the second resistor of the voltage divider.
Dependencies are inferred from the claim text.