Driver for a power field-effect transistor with a programmable drive voltage, and related systems and methods

An LLC resonant converter, comprising:

• a half-bridge circuit including a phase node;
• a half bridge driver coupled to drive the half-bridge circuit;
• a transformer including a primary winding coupled to phase node of the half-bridge circuit and including first and second secondary windings coupled to and output node;
• a resonant inductor and resonant capacitor coupled to the primary winding;
• first and second synchronous rectifier switches coupled in series with the first and second secondary windings;
• and
• a synchronous rectifier driver including a driver coupled to drive the first and second rectifier switches, the synchronous rectifier driver including a supply voltage node configured to receive a supply voltage and a gate drive node configured to be coupled to a gate node of a power transistor, the synchronous rectifier driver further including for each synchronous rectifier switch a high-side driver transistor coupled between the supply voltage node and the gate drive node and including a high side gate node, the synchronous rectifier driver configured to operate, in response to an activation signal going active, in a first mode to provide a first charge current to the high side gate node until a gate drive voltage on the gate drive node reaches a first gate drive threshold, the synchronous rectifier driver configured to then operate in a second mode responsive to the gate drive voltage reaching the first gate drive threshold to provide a second charge current to the high side gate node that is less than the first charge current and to limit the gate drive voltage to a first clamped threshold, the synchronous rectifier driver configured to receive a gate drive current rise signal that sets the value of the second charge current and further configured to operate in the second mode for a delay time after the gate drive voltage reaches the first gate drive threshold, and the synchronous rectifier driver further configured, after expiration of the delay time, to operate in a third mode to provide the second charge current to the high side gate node and to limit the gate drive voltage to a second clamped threshold that is greater than the first clamped threshold but less than the supply voltage, the synchronous rectifier driver configured to receive a gate drive programmable control signal that sets the value of the second clamped threshold.

A method, comprising:

• providing a first charge current to a high side control node of a high-side driver transistor coupled between a supply voltage node configured to receive a supply voltage and a control drive node;
• providing a drive current from the supply voltage node through the high-side driver transistor to the control drive node responsive to a voltage generated on the high side control node responsive to the first charge current;
• sensing a control drive voltage generated on the control drive node in response to the drive current;
• detecting whether the control drive voltage has reached a first control drive threshold;
• providing a second charge current to the high side control node in response to detecting the voltage on the control drive node has reached the first control drive threshold, the second charge current being less than the first charge current and the second charge current being provided for a delay time after detecting the control drive voltage has reached the first control drive threshold;
• limiting the control drive voltage to a first clamped threshold during the delay time while providing the second charge current to the high side control node;
• providing the second charge current to the high side control node after expiration of the delay time;
• and
• limiting the control drive voltage to a second clamped threshold that is greater than the first clamped threshold but less than the supply voltage after expiration of the delay time while providing the second charge current to the high side control node.