FIELD OF THE DISCLOSURE

Embodiments of the invention relate to electronic systems, and more particularly, to charge pumps.

BACKGROUND

A voltage regulator serves to generate a substantially constant output voltage from a poorly-specified and/or fluctuating supply voltage or other input voltage source. Series regulators and switching regulators are two common types of voltage regulators. Low dropout (LDO) series regulators provide good regulation with very low noise, however, the current supply from the regulated output comes directly from the supply voltage. Thus, an LDO series regulator's efficiency is limited by the ratio of the output voltage to the supply voltage, and thus the efficiency of the LDO series regulator drops rapidly as the supply voltage increases relative to the output voltage.

Switching regulators are generally more efficient than series regulators. A switching regulator employs one or more switches (for instance, power transistors) coupled in series and/or parallel with an output terminal that provides an output voltage to a load. Additionally, a control circuit (for instance, an oscillator) turns the switches ON and OFF to control delivery of current pulses to the output terminal. One or more energy storage elements, such as inductor(s) and/or capacitor(s), can be used to convert the switched current pulses into a steady load current. Because inductors suitable for voltage regulation tend to be large components, switched capacitor converters are preferred in miniaturized devices, for instance, applications in which it is desired to fully integrate a switching regulator on a semiconductor die.

SUMMARY OF THE DISCLOSURE

Charge pumps with accurate output current limiting are provided herein. In certain embodiments, a charge pump includes an output terminal for providing a regulated output voltage, a switched capacitor, and switches that control connectivity of the switched capacitor to selectively charge or discharge the switched capacitor. The switches are operable in two or more phases including a charging phase in which the switched capacitor is charged with a charging current and a discharging phase in which the switched capacitor is coupled to the output terminal. The charge pump further includes an output current limiting circuit that limits an amount of output current delivered by the charge pump to the output terminal during the discharging phase. The output current limiting circuit limits the output current based on comparing a reference signal to an integral of an observation current that changes in relation to the charging current. For instance, when the charge provided to the switched capacitor during the charging phase is limited, a corresponding amount of charge that is discharged during the discharging phase is also constrained. By controlling the amount of output charge for a given switching frequency of the charge pump, the amount of output current is accurately limited. Controlling an amount of output current delivered by the charge pump to a load provides a number of advantages, such as maintaining the load within operating parameters and/or constraints.

In one aspect, a charge pump with accurate output current limiting is provided. The charge pump includes a switched capacitor and a plurality of switches configured to control connectivity of the switched capacitor. The plurality of switches are operable in two or more phases including a charging phase in which the switched capacitor is charged by a charging current and a discharging phase in which the switched capacitor is coupled to an output terminal. The charge pump further includes an output current limiting circuit configured to control the charging current to limit an amount of output current to the output terminal. The output current limiting circuit is configured to generate an integration signal based on integrating an observation current that changes in relation to the charging current, and to control the charging current based on comparing the integration signal to a reference signal.

In another aspect, a method of accurately limiting an output current of a charge pump is provided. The method includes providing a charging current to a switched capacitor in a charging phase of the charge pump, connecting the switched capacitor to an output terminal in a discharging phase of the charge pump, and controlling the charging current to limit an amount of output current to the output terminal, including integrating an observation current that changes in relation to the charging current, comparing the integrated observation current to a reference signal, and controlling the charging current based on the comparison.

In another aspect, a current source with accurate current limiting is provided. The current source includes a current mirror configured to receive a reference current and to generate a charging current and an observation current, the observation current changing in relation to the charging current. The current source further includes a current limiting circuit configured to generate an integration signal based on integrating the observation current, and to control the reference current based on comparing the integration signal to a reference signal.

