Method for controlling the operation of a low-dropout voltage regulator and corresponding integrated circuit
An integrated circuit including at least one low-dropout voltage regulator (LDO) capable of delivering a regulated output voltage using a reference voltage (VREF), comprises means for generating a substitution voltage (VRMP) in the form of a ramp and control means capable of replacing the reference voltage (VREF) by the substitution voltage as long as the substitution voltage (VRMP) is lower than the reference voltage (VREF).
1. A method for controlling a regulated output voltage, the method comprising:
delivering a regulated output voltage using a reference voltage via at least one low-dropout voltage regulator;
replacing the reference voltage with a substitution voltage in a form of a ramp, as long as a value of the substitution voltage remains below the reference voltage during a start-up phase for the low-dropout voltage regulator;
coupling an output of the low-dropout voltage regulator to a load that is in parallel with an external capacitor; and
adjusting a slope of the ramp of the substitution voltage as a function of a desired current flowing through the external capacitor during the start-up phase.
2. The method according to claim 1 , further comprising:
coupling the reference voltage to a first input of a first operational amplifier;
coupling an output of the first operational amplifier back into a second input of the first operational amplifier via a control transistor; and
wherein the replacing includes using a second operational amplifier having a first input connected to the substitution voltage, a second input connected to a second input of the first operational amplifier and an output connected to the output of the first amplifier and to a gate of the control transistor.
3. The method according to claim 1 , further comprising:
coupling a first input of a first operational amplifier to the reference voltage;
coupling an output of the first operational amplifier back into a second input of the first operational amplifier via a control transistor; and
wherein the replacing includes using a comparator capable of comparing the substitution voltage and the reference voltage; and using a switch, connected to the first input of the first operational amplifier, the switch capable of delivering one of the substitution voltage and the reference voltage, depending on an output signal delivered by the comparator.
4. The method according to claim 1 , further comprising:
coupling a gate of a first transistor of a first operational amplifier to the reference voltage;
wherein the replacing includes using an additional transistor mounted in parallel with the first transistor of the first operational amplifier, the additional transistor with a gate coupled to the substitution voltage.
5. The method according to claim 2 , wherein the first operational amplifier comprises two PMOS input transistors.
6. The method according to claim 3 , wherein the first operational amplifier comprises two PMOS input transistors.
7. The method according to claim 4 , wherein the first operational amplifier comprises two PMOS input transistors.
8. An integrated circuit for controlling a regulated output voltage, the integrated circuit comprising:
at least one low-dropout voltage regulator capable of delivering a regulated output voltage using a reference voltage, wherein the low-dropout voltage regulator includes:
means for generating a substitution voltage in a form of a ramp; and
means for controlling a replacement of the reference voltage by the substitution voltage as long as the substitution voltage is lower than the reference voltage during a start-up phase,
wherein an output of the low-dropout voltage regulator is connected to a load that is in parallel with an external capacitor, and wherein a slope of the ramp of the substitution voltage is a function of a desired current flowing through the external capacitor during the start-up phase.
9. The integrated circuit according to claim 8 , wherein the low-dropout voltage regulator further comprises:
a first operational amplifier having a first input receiving the reference voltage and an output fed back into a second input of the first operational amplifier via a control transistor; and
wherein the control means comprise a second operational amplifier having a first input connected to the output of the means of generating a substitution voltage, a second input connected to a second input of the first operational amplifier and an output connected to the output of the first amplifier and to a gate of the control transistor.
10. The integrated circuit according to claim 8 , wherein the low-dropout voltage regulator further comprises:
a first operational amplifier having a first input receiving the reference voltage and an output fed back into a second input of the first operational amplifier via a control transistor; and
wherein the control means comprise a second operational amplifier having a first input connected to the output of the means of generating a substitution voltage, a second input connected to a second input of the first operational amplifier and an output connected to the output of the first amplifier and to a gate of the control transistor.
11. The integrated circuit according to claim 8 , wherein the low-dropout voltage regulator further comprises:
a first operational amplifier having a first input receiving the reference voltage, and an output fed back into a second input of the first operational amplifier via a control transistor, and
wherein in that the control means comprise:
a comparator capable of comparing the substitution voltage and the reference voltage; and
a switch, connected to the first input of the first operational amplifier, the switch capable of delivering one of the substitution voltage and the reference voltage, depending on an output signal delivered by the comparator.
12. The integrated circuit according to claim 8 , wherein the low-dropout voltage regulator further comprises:
a first operational amplifier having a first input receiving the reference voltage, and an output fed back into a second input of the first operational amplifier via a control transistor, and
wherein in that the control means comprise:
a comparator capable of comparing the substitution voltage and the reference voltage; and
a switch, connected to the first input of the first operational amplifier, the switch capable of delivering one of the substitution voltage and the reference voltage, depending on an output signal delivered by the comparator.
13. The integrated circuit according to claim 8 , wherein the low-dropout voltage regulator further comprises:
a first operational amplifier comprising a first transistor with a gate coupled to the reference voltage;
wherein the control means includes an additional transistor mounted in parallel with the first transistor of the first operational amplifier, the additional transistor with a gate coupled to the substitution voltage.
14. The integrated circuit according to claim 8 , wherein the low-dropout voltage regulator further comprises:
a first operational amplifier comprising a first transistor with a gate coupled to the reference voltage;
wherein the control means includes an additional transistor mounted in parallel with the first transistor of the first operational amplifier, the additional transistor with a gate coupled to the substitution voltage.
15. The integrated circuit according to claim 13 , wherein the first operational amplifier comprises two PMOS input transistors.
16. The integrated circuit according to claim 14 , wherein the first operational amplifier comprises two PMOS input transistors.