Driver circuitry and operation

A driver apparatus for driving a transducer in a bridge-tied-load configuration based on an input signal comprising:

• first and second input nodes for receiving first and second supply voltages respectively defining an input voltage;
• a first charge pump configured to generate a first boosted voltage which is positively boosted from the first supply voltage;
• a second charge pump configured to generate a second boosted voltage which is negatively boosted from the second supply voltage;
• an output bridge stage with first and second driver output nodes for connection to opposite sides of the load, wherein the output bridge stage comprises a switch network for selectively connecting each of the first and second driver output nodes to any of the first supply voltage, the second supply voltage, the first boosted voltage or the second boosted voltage;
• and
• a controller configured to control the switch network of the output bridge stage to selectively operate in each of:
• a first driver mode in which each of the first and second output nodes is modulated between the first and second supply voltage;
• a second driver mode in which one of the first and second output nodes is modulated between the first and second supply voltages and the other of the first and second output nodes is modulated between either the first boosted voltage and the first supply voltage or between the second supply voltage and the second boosted voltage;
• and
• a third driver mode in which one of the first and second output nodes is modulated between the first supply voltage and the first boosted voltage and the other of the first and second output node is modulated between the second supply voltage and the second boosted voltage;
• wherein the controller is configured to control the driver mode and a duty cycle of the modulation in said driver mode based on the input signal.