Floating trickle charge pump with auto turn-off and auto turn-on
A high-side driver-circuit involves a charge-pump for driving a high-side transistor. The circuit includes a high-side transistor, a low-side transistor or unidirectional conducting-device, a bootstrap-capacitor, and a trickle-charge-pump connected between the output-node and ground. The trickle-charge-pump activates when the voltage at the output-node exceeds the voltage at the low-voltage power-supply-node, alternately charging a trickle-capacitor and transferring charge to the bootstrap-capacitor. This enables continuous replenishment of the bootstrap-capacitor, allowing for extended or indefinite high-side conduction periods, including 100% duty-cycle operation. The trickle-charge-pump incorporates an auto-on/auto-off functionality, synchronizing operation with the output-node-voltage. It activates when the voltage at the output-node exceeds the voltage at the low-voltage power-supply-node and deactivates when the voltage at the output-node is less than the voltage at the low-voltage power-supply-node, enhancing overall efficiency. This design overcomes limitations of traditional bootstrap circuits without added complexity, providing an efficient approach for applications requiring sustained high-side operation in high-side driver circuits.
1 . A half-bridge driver circuit, comprising:
a half-bridge including: a high-side transistor connected between a voltage supply and an output node, and a low-side transistor connected between the output node and a reference node;
a bootstrap capacitor connected between a bootstrap node and the output node;
a high-side driver circuit configured to drive a control terminal of the high-side transistor; and
a trickle charge pump connected between the output node and ground, the trickle charge pump configured to charge the bootstrap capacitor during high-side conduction periods and/or when a voltage at the output node exceeds a voltage at a low voltage power supply node, wherein the trickle charge pump comprises:
a floating low-voltage supply powered between the output node and ground;
an oscillator powered between the output node and a voltage generated by the floating low-voltage supply;
a buffer powered between the output node and the voltage generated by the floating low-voltage supply, and coupled to receive an oscillator signal output from the oscillator;
a trickle capacitor connected between an output of the buffer and an intermediate node;
a first unidirectional conduction device connected between the output node and the intermediate node; and
a second unidirectional conduction device connected between the intermediate node and the bootstrap node;
wherein the trickle charge pump is configured to operate, when the voltage at the output node exceeds the voltage at the low voltage power supply node, in:
a first phase wherein the trickle capacitor is charged through the first unidirectional conduction device; and
a second phase wherein charge is transferred from the trickle capacitor to the bootstrap capacitor through the second unidirectional conduction device.
2 . The half-bridge driver circuit of claim 1 , wherein the trickle charge pump includes an auto-on/auto-off functionality that activates the trickle charge pump when the voltage at the output node exceeds the voltage at the low voltage power supply node and deactivates the trickle charge pump when the voltage at the output node is less than the voltage at the low voltage power supply node, wherein: the trickle charge pump is powered by the voltage at the output node, with activation occurring when the voltage at the output node exceeds the voltage at the low voltage power supply node; and the auto-off functionality occurs when the voltage at the output node is less than the voltage at the low voltage power supply node.
3 . The half-bridge driver circuit of claim 1 , further comprising: a level shifter configured to provide a pre-drive signal to the high-side driver circuit based on a high-side input signal; and a low-side driver circuit configured to drive the low-side transistor based on a low-side input signal.
4 . The half-bridge driver circuit of claim 1 , wherein the trickle charge pump is configured to enable 100% duty cycle operation of the high-side transistor by continuously replenishing charge in the bootstrap capacitor when the voltage at the output node exceeds the voltage at the low voltage power supply node.
5 . A half-bridge driver circuit, comprising:
a half-bridge including: a high-side transistor connected between a voltage supply and an output node, and a low-side transistor connected between the output node and a reference node;
a bootstrap capacitor connected between a bootstrap node and the output node;
a high-side driver circuit configured to drive the high-side transistor; and
a trickle charge pump connected between the output node and ground, wherein the trickle charge pump is configured to: activate when a voltage at the output node exceeds a voltage at a low voltage power supply node, and alternately charge a trickle capacitor and transfer charge from the trickle capacitor to the bootstrap capacitor when the voltage at the output node exceeds the voltage at the low voltage power supply node.
6 . The half-bridge driver circuit of claim 5 , wherein the trickle charge pump is further configured to: deactivate when the voltage at the output node is less than the voltage at the low voltage power supply node.
7 . The half-bridge driver circuit of claim 5 , wherein the trickle charge pump is powered by the voltage at the output node.
8 . The half-bridge driver circuit of claim 5 , wherein the trickle charge pump is configured to enable 100% duty cycle operation of the high-side transistor by continuously replenishing charge in the bootstrap capacitor when the voltage at the output node exceeds the voltage at the low voltage power supply node.
9 . The half-bridge driver circuit of claim 5 , further comprising: a level shifter configured to provide a pre-drive signal to the high-side driver circuit based on a high-side input signal; and a low-side driver circuit configured to drive the low-side transistor based on a low-side input signal.
10 . The half-bridge driver circuit of claim 5 , wherein the trickle charge pump comprises:
a floating low-voltage supply powered between the output node and ground;
an oscillator powered between the output node and a voltage generated by the floating low-voltage supply;
a buffer powered between the output node and the voltage generated by the floating low-voltage supply, and coupled to receive an oscillator signal output from the oscillator;
the trickle capacitor connected between an output of the buffer and an intermediate node;
a first unidirectional conducting device connected between the output node and the intermediate node; and
a second unidirectional conducting device connected between the intermediate node and the bootstrap node.
11 . A method of operating a high-side driver circuit, the method comprising:
driving a high-side transistor to generate a voltage when an output node exceeds a voltage at a low voltage power supply node;
activating a trickle charge pump connected between the output node and ground when the voltage at the output node exceeds the voltage at the low voltage power supply node; and
alternately charging a trickle capacitor and transferring charge from the trickle capacitor to a bootstrap capacitor using the trickle charge pump when the voltage at the output node exceeds the voltage at the low voltage power supply node, wherein the bootstrap capacitor is connected between a bootstrap node and the output node.
12 . The method of claim 11 , further comprising:
driving a low-side transistor of the high-side driver circuit to generate a voltage at the output node that is less than the voltage at the low voltage power supply node; and
deactivating the trickle charge pump when the voltage at the output node is less than the voltage at the low voltage power supply node.
13 . The method of claim 12 , wherein deactivating the trickle charge pump comprises connecting the output node to ground through the low-side transistor or a unidirectional conducting device.
14 . The method of claim 11 , wherein activating the trickle charge pump comprises powering the trickle charge pump using the voltage at the output node.
15 . The method of claim 11 , wherein alternately charging the trickle capacitor and transferring charge comprises: charging the trickle capacitor through a first unidirectional conducting device connected between the output node and the trickle capacitor during a first phase; and discharging the trickle capacitor through a second unidirectional conducting device connected between the trickle capacitor and the bootstrap node during a second phase.
16 . The method of claim 11 , further comprising: continuously replenishing charge in the bootstrap capacitor when the voltage at the output node exceeds the voltage at the low voltage power supply node to enable 100% duty cycle operation of the high-side transistor.
17 . The method of claim 11 , further comprising: level-shifting a high-side input signal to generate a pre-drive signal; and providing the pre-drive signal to a high-side driver circuit to drive the high-side transistor.
18 . The method of claim 11 , further comprising:
generating a voltage at the output node that is less than the voltage at the low voltage power supply node using a diode; and
deactivating the trickle charge pump when the voltage at the output node is less than the voltage at the low voltage power supply node.