Low drop-out voltage regulator and a method of providing a regulated voltage

1. A low drop-out voltage regulator for providing a regulated voltage, the low drop-out voltage regulator comprises

a supply voltage terminal for receiving a supply voltage;

a regulated voltage terminal for providing the regulated voltage;

a regulated voltage driver for providing the regulated voltage to the regulated voltage terminal in response to a control voltage;

a feedback-loop circuit for generating the control voltage on basis of a feedback voltage such that the regulated voltage driver provides the regulated voltage wherein, in the feedback-loop circuit, a first feedback voltage is generated which relates to the value of the regulated voltage on basis of a first ratio between the first feedback voltage and the regulated voltage;

a pull-up circuit for pulling the regulated voltage up to the supply voltage when a difference between the supply voltage and the control voltage is smaller than a predefined voltage difference, wherein

the pull-up circuit is configured to provide a pull-up signal to the feedback-loop circuit when the regulated voltage is pulled up to the supply voltage, and

the feedback-loop circuit is configured to generate a second feedback voltage instead of the first feedback voltage when it receives the pull-up signal the second feedback voltage is generated on basis of a second ratio between the second feedback voltage and the regulated voltage, the second ratio is different from the first ratio and the second ratio is for preventing oscillations in the low drop-out voltage regulator.

2. A low drop-out voltage regulator according to claim 1 , wherein the first ratio is larger than the second ratio.

3. A low drop-out voltage regulator according to claim 1 , wherein the first feedback voltage and the second feedback voltage directly relate to a voltage of the regulated voltage terminal according to, respectively, the first ratio and the second ratio.

4. A low drop-out voltage regulator according to claim 3 , wherein a terminal of the feedback-loop circuit is coupled to the regulated voltage terminal for generating the first feedback voltage and the second feedback voltage.

5. A low drop-out voltage regulator according to claim 1 , wherein the feedback-loop circuit comprises a first operational amplifier for comparing a reference voltage coupled to the plus input port with the feedback voltage coupled to the minus input port, wherein the first operational amplifier generates the control voltage.

6. A low drop-out voltage regulator according to claim 1 , wherein the regulated voltage driver comprises a driving transistor being coupled between the supply voltage and the regulated voltage terminal, a gate of the driving transistor receives the control voltage.

7. A low drop-out voltage regulator according to claim 1 , wherein the feedback-loop circuit comprises a series arrangement of a first resistor, a second resistor and a third resistor, the first resistor being coupled to the regulated voltage terminal and the third resistor being coupled to a ground voltage, the first feedback voltage according to the first ratio is present at a terminal shared by the first resistor and the second resistor and the second feedback voltage according to the second ratio is present at a terminal shared by the second resistor and the third resistor.

8. A low drop-out voltage regulator according to claim 7 , wherein the feedback-loop circuit comprises a first controllable switch and a second controllable switch, a first terminal of the first controllable switch is coupled to the terminal shared by the first resistor and the second resistor and a second terminal of the first controllable switch is coupled to a feedback terminal that provides the feedback voltage, a first terminal of the second controllable switch is coupled to the terminal shared by the second resistor and the third resistor and a second terminal of the second controllable switch is also coupled to the feedback terminal, wherein the feedback-loop circuit is configured to control the first controllable switch in a conducting mode and to control the second controllable switch in a non-conducting mode when no pull-up signal is received, and feedback-loop circuit is configured to control the first controllable switch in a non-conducting mode and to control the second controllable switch in a conducting mode when the pull-up signal is received.

9. A low drop-out voltage regulator according to claim 8 , wherein the first controllable switch and the second controllable switch are, respectively, a first transistor and a second transistors and the pull-up signal is provided directly to a gate of the second transistor and an inverted pull-up signal is provided to a gate of the first transistor.

10. A low drop-out voltage regulator according to claim 7 , wherein the second resistor has a second resistance R 2 , the third resistor has a third resistance R 3 and

R

⁢

⁢

3

<

R

⁢

⁢

2

⁢

V

sup

Vsup

pull

-

up

-

sustfed

max

-

V

reg

,

wherein V reg is the required regulated voltage and Vsup pull-up enabled max is the maximum supply voltage at which it can occur that the pull-up circuit pulls the regulated voltage up to the supply voltage.

11. A low drop-out voltage regulator according to claim 1 , wherein the low drop-out voltage regulator is an open-loop voltage regulator and comprises an regulated output voltage terminal, wherein

the regulated voltage driver generates the regulated voltage of the regulated voltage terminal and generates an regulated output voltage at the regulated output voltage terminal on basis of the control voltage.

12. A low drop-out voltage regulator according to claim 11 , wherein

the regulated voltage driver comprises an internal regulated voltage transistor and an output regulated voltage transistor, the internal regulated voltage transistor being coupled between the supply voltage and the regulated voltage terminal for providing the regulated voltage to the regulated voltage terminal, a gate of the internal regulated voltage transistor receives the control voltage, the output regulated voltage transistor being coupled between the supply voltage and the regulated output voltage terminal for providing the regulated output voltage, a gate of the output regulated voltage transistor receives the control voltage.

13. A low drop-out voltage regulator according to claim 1 , wherein the low drop-out voltage regulator is a closed-loop voltage regulator wherein a regulated output voltage of the low drop-out voltage regulated is provided by the regulated voltage terminal.

14. A low drop-out voltage regulator according to claim 1 , wherein the pull-up circuit comprises a second operational amplifier for generating the pull-up signal, the plus input port of the second operational amplifier is coupled to the supply voltage and the minus input port of the second operational amplifier is coupled to the control voltage, wherein the second operational amplifier has a build-in offset voltage being substantially equal to the predefined voltage difference.

15. A method of providing a regulated voltage, the method comprises:

generating a control voltage by a feedback-loop circuit for controlling a regulated voltage driver that provides the regulated voltage;

generating the regulated voltage by the regulated voltage driver in dependence of the control voltage;

pulling-up the regulated voltage to a supply voltage when a difference between the supply voltage and the control voltage is smaller than predefined voltage difference;

generating in the feedback-loop circuit a first feedback voltage or a second feedback voltage which relate to the regulated voltage on basis of a first ratio between the first feedback voltage and the regulated voltage or on basis of a second ratio between the second feedback voltage and the regulated voltage, wherein the first ratio is different from the second ratio and wherein the first feedback voltage is generated on basis of the first ratio when the regulated voltage is not pulled-up to the supply voltage and the second feedback voltage is generated on basis of the second ratio when the regulated voltage is pulled-up to the supply voltage.