Charge-pump closely coupled to switching converter

Details Charge-pump closely coupled to switching converter Charge-pump closely coupled to switching converter

1999-09-04

2001-03-13

Riley, Shawn (Department: 2838)

Electric power conversion systems

Current conversion

With voltage multiplication means

C363S016000, C363S131000

Reexamination Certificate

active

06201717

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to integrated circuits, and more specifically to a charge pump circuit for a switching converter.
BACKGROUND OF THE INVENTION
As logic integrated circuits (ICs) have migrated to lower working voltages in the search for lower power consumption and higher operating frequencies, and as overall system sizes have continued to decrease, IC power supply designs with smaller size and higher efficiency are in demand. Switch mode power supplies, or DC to DC converters, as they are sometimes called, are frequently used in IC circuits such as digital signal processors (DSPs) and mixed signal analog circuits, etc., to efficiently convert an input supply voltage to voltage levels appropriate for internal circuitry as well as external circuitry that the IC is coupled to. For instance, a 2.8 volt supply voltage provided to a BiCMOS IC may need to be increased internally to 5.0 volts to operate internal CMOS circuitry. As appliances and circuit designs continue to decrease in size, the need for smaller and more efficient IC switch mode power converters increases.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a charge pump adapted for use in a circuit, the charge pump having switches driven by a voltage higher than an input voltage to the circuit, resulting in the ability to use smaller NMOS FETs as switches, saving semiconductor real estate.
In one embodiment, a circuit is adapted to receive an input voltage, including a means of producing a second voltage higher than the input voltage, the means being integral to the circuit. The circuit includes a plurality of switches coupled together in a charge pump arrangement, including a first switch, where at least the first switch is driven by the second voltage. The first switch may be driven by a first driver, and another of the switches may be a second switch driven by a second driver. The charge pump arrangement may be adapted to provide a bootstrap voltage at a bootstrap voltage terminal and a drive voltage for a switch mode power supply. The higher voltage may be obtained from a voltage at a node between an additional switch and an additional capacitor, or alternatively, the higher voltage may be obtained from the bootstrap voltage.
In another embodiment, a switch mode power converter powered by a charge pump circuit includes a first, second, third, fourth and fifth switch coupled together in a charge pump circuit. The first switch is connected to an input voltage terminal and is driven by a first driver. The second switch is connected to an input voltage terminal and is driven by a second driver. The charge pump arrangement provides a bootstrap voltage at a boot voltage terminal for a third driver and a drive voltage at a drive voltage terminal to a fourth driver. A first capacitor is coupled between the drive voltage terminal and a ground terminal. The first transistor is driven by the first driver and is coupled to the input voltage terminal and a phase node. The second capacitor is connected at one end to the bootstrap voltage terminal and at the other end to the phase node. A second transistor is coupled to the output of the second driver, the phase node and the ground terminal. At least the first driver is powered by a voltage higher than the input voltage at the input voltage terminal. The higher voltage may be obtained from a voltage at a node between an additional switch and an additional capacitor, or alternatively, the higher voltage may be obtained from the bootstrap voltage.
Also disclosed is a method of reducing the lateral semiconductor area of a charge pump circuit. The method includes the step of providing a plurality of switches coupled together in a charge pump arrangement, where the charge pump arrangement is adapted to provide a bootstrap voltage at a boot voltage terminal for a switch mode power supply. The plurality of switches includes at least a first switch and a second switch coupled to an input voltage terminal. The first and second switches are driven by a first driver and a second driver, respectively. The method includes the step of powering at least first driver with a voltage higher than input voltage. The higher voltage may be obtained from a voltage at a node between an additional switch and an additional capacitor, or alternatively, the higher voltage may be obtained from the bootstrap voltage.
Advantages of the present invention include at least one driver of a switch in the charge pump circuit being powered by a voltage higher than the input voltage of the circuit, which allows NMOS FETs to be used for the majority of the switches in the charge pump circuit, resulting in semiconductor real estate savings of one-half to on-third. Another advantage of the present invention is that noise generated by the charge pump is inherently synchronous to the main switching converter, which reduces the likelihood that charge pump noise will interfere with the main converter. A further advantage of the present invention is that the main load of the charge pump is the gate charge required for the main switching converter power FETs, synchronizing the charge pump to the main converter, making the charge pump output approximately track the demand. Also, the second embodiment of the present invention requires no additional components to achieve a bootstrap voltage higher than the input voltage powering the driver of the first switch.


REFERENCES:
patent: 4803612 (1989-02-01), Skovmand
patent: 5627460 (1997-05-01), Bazinet et al.
patent: 5818209 (1998-10-01), Masini et al.

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