DC-DC converter with low start-up power and voltage

Patent metadata

Field	Value
Publication number	US-9742271-B2
Application number	US-201615167073-A
Country	US
Kind code	B2
Filing date	May 27, 2016
Priority date	Jun 5, 2015
Publication date	Aug 22, 2017
Grant date	Aug 22, 2017

Abstract

A DC-DC converter ( 1 ) with low start-up power and voltage includes an inductor ( 3 ) connected to an input voltage source ( 2 ), a switch ( 11 ) connected to the inductor and controlled by a controller ( 10 ) and a diode ( 12 ) connected to a connection node of the inductor and the switch to provide an output voltage (Vout). The controller includes an oscillator and a monostable element, which are powered by the input voltage (Vin). The oscillator provides an oscillation signal (OSC) having a period T of a switching cycle of the switch. The monostable element ( 103 ) is controlled by the oscillation signal to determine a duration Tn of conduction of the switch, during which an increasing current (IL) flows through the inductor. The input impedance of the DC-DC converter increases, when the input voltage (Vin) drops below a first voltage threshold with a decreasing duty cycle d=Tn/T.

First claim

What is claimed is:

1. A DC-DC converter with low start-up power and voltage and operating in discontinuous mode, the converter including an inductor for connection to a power source providing an input voltage to be converted, a switch connected to the inductor and controlled by a controller and a diode element connected to a connection node of the inductor and the switch to provide an output voltage,
wherein the controller includes at least an oscillator and a monostable element, which are powered by the input voltage provided by the power source,
wherein the oscillator is configured to provide an oscillation signal, whose oscillation period determines a period T of one switching cycle of the switch,
wherein the monostable element is configured to receive the oscillation signal from the oscillator in order to determine a first duration Tn of conduction of the switch, during which an increasing current flows through the inductor, and
wherein, depending on the constituent elements of the oscillator and of the monostable element, a duty cycle d=Tn/T between the first duration of conduction of the switch and the oscillation period of the oscillator decreases, when the input voltage decreases with an increase in the input impedance of the DC-DC converter.

2. The DC-DC converter according to claim 1 , wherein the oscillator is a ring oscillator, which includes a number N of successive inverter stages, where N is an integer odd number greater than 1, the last inverter stage being connected in a loop to the first inverter stage.

3. The DC-DC converter according to claim 2 , wherein the number N of inverter stages is equal to 5, and wherein an output inverter is connected to the last inverter stage to provide the oscillation signal.

4. The DC-DC converter according to claim 2 , wherein each inverter stage includes an RC network, which is formed of a resistor and a capacitor connected to a corresponding inverter.

5. The DC-DC converter according to claim 4 , wherein each inverter includes a PMOS transistor mounted in series with an NMOS transistor between an internal input voltage terminal of the oscillator and an earth terminal, wherein the resistor is connected on one hand to gates of the two PMOS and NMOS transistors of the same stage, and on the other hand to drains of the PMOS and NMOS transistors of a preceding stage, and wherein the capacitor is connected between the gates of the PMOS and NMOS transistors and the earth terminal.

6. The DC-DC converter according to claim 1 , wherein the monostable element includes a number M of successive delay stages, wherein M is an integer number greater than or equal to 1, for the determination of the first duration Tn of actuation of the switch.

7. The DC-DC converter according to claim 6 , wherein the number M of delay stages is equal to 3.

8. The DC-DC converter according to claim 6 , wherein each delay stage includes an inverter, which is formed of a PMOS transistor mounted in series with an NMOS transistor between an internal input voltage terminal of the monostable element and an earth terminal and an RC input network, and wherein the RC network includes a resistor between an input of each stage and connected gates of the PMOS and NMOS transistors, and a capacitor connected to the gates of the PMOS and NMOS transistors and to the earth terminal, and wherein an output of each stage is a connection node of the drains of the PMOS and NMOS transistors.

9. The DC-DC converter according to claim 6 , wherein each delay stage further includes an RS flip-flop receiving, at a first input, the oscillation signal from the oscillator and, at a second input, an output signal from the last delay stage in order to provide, at output, a control signal for the determination of the first duration Tn.

10. The DC-DC converter according to claim 9 , wherein the first delay stage receives the oscillation signal from the oscillator via an input inverter, wherein the second input of the RS flip-flop receives an output signal from the last delay stage via an intermediate non-inverter, and wherein the control signal is provided at the monostable element output from the RS flip-flop output via a non-inverter of output.

11. The DC-DC converter according to claim 1 , wherein the switch is a MOS transistor, such as an NMOS transistor, connected between the inductor and an earth terminal, whose gate receives a control signal from the controller for control of the first duration Tn of conduction of the MOS transistor, and wherein the diode element is a Schottky diode connected between a connection node of the inductor and of the MOS transistor and an output terminal of the DC-DC converter.

12. The DC-DC converter according to claim 1 , wherein the controller includes a phase generator controlled by a control signal from the monostable element, and an internal charge pump, which is clocked by two phase signals from the phase generator, and controls, via a control signal, the switch, which is a MOS transistor.

13. The DC-DC converter according to claim 12 , wherein the controller includes an input switch, which is a PMOS transistor, whose source is connected to an input voltage terminal of the converter to receive the input voltage from the power source, and a drain for providing the internal input voltage for the oscillator, the monostable element, the phase generator and the internal charge pump, wherein a gate of the PMOS transistor is controlled by an input signal from an external unit from an input terminal of the controller, in order to make the PMOS transistor conductive for the operation of the controller, or non-conductive in a pause mode of the controller.

14. The DC-DC converter according to claim 13 , wherein the controller also includes a first NMOS transistor, which is connected between the internal input voltage line and the earth terminal, and a second NMOS transistor, which is connected between the gate of the NMOS transistor and the earth terminal, wherein gates of the first and second NMOS transistors are connected to the gate of the PMOS transistor in order to be made conductive by the input signal from the external unit, when the PMOS transistor is non-conductive, and vice versa.

15. The DC-DC converter according to claim 1 , wherein at least the controller and the switch of a main block of the DC-DC converter are made in the same integrated circuit in CMOS technology.

16. The DC-DC converter according to claim 1 , wherein the duty cycle d=Tn/T between the first period Tn of conduction of the switch and the oscillation period T of the oscillator decreases with an increase in period T, when the input voltage drops below a first low voltage threshold.

17. The DC-DC converter according to claim 16 , wherein the first duration Tn increases, when the input voltage drops below a second low voltage threshold lower than the first voltage threshold.

18. The DC-DC converter according to claim 17 , wherein the first voltage threshold is around 0.45 V, and wherein the second voltage threshold is around 0.3 V.

19. The DC-DC converter according to claim 17 , wherein the monostable element transistors are made in wider dimensions than the oscillator transistors in order to obtain an increase in the first duration Tn with respect to an increase in the oscillation period T at a lower input voltage.

20. A method for actuation of a DC-DC converter according to claim 1 , wherein the converter with low start-up power and voltage operates in discontinuous mode and includes an inductor for connection to a power source providing an

Assignees

• Em Microelectronic-Marin S A
• Em Microelectronic Marin Sa

Inventors

• Theoduloz Yves
• Saby Jerome
• Marti Cyril

Classifications

• H02M1/36

  Means for starting or stopping converters · CPC title

• H02M3/156 Primary

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title