Pre-Driven Bootstrap Gate Driver for Smaller High-Side Capacitors
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Solution Overview
Problem
Existing bootstrapping gate driver circuits require large bootstrap capacitors and small resistors, leading to high power consumption and large capacitor area requirements.
Innovation Solution
A pre-driven bootstrapping gate driver circuit that applies an initial pre-driven voltage to the gate-to-source of the high side FET before the bootstrap capacitor releases charge, reducing the required capacitance and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bootstrapping gate driver circuits are used, then the gate voltage can be maintained above supply voltage, but large bootstrap capacitors are required leading to large area requirements
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate-to-source capacitance of the high side FET to a pre-driven voltage (e.g., 0.5Vdd to 0.8Vdd) before the bootstrap capacitor needs to charge it fully. This pre-charging is achieved through a pre-driven FET that turns on before the main high side FET, reducing the voltage swing the bootstrap capacitor must provide and thereby reducing its required capacitance and area by up to 66.7%
2Reliability
If conventional bootstrapping gate driver circuits are used, then the gate voltage can be maintained above supply voltage, but high power consumption occurs due to small resistor values
Solution Approach 1:
The pre-driven FET performs preliminary action by establishing the initial gate voltage before the main switching action occurs. This reduces the discharge current through the resistor during normal operation, thereby reducing power consumption while maintaining reliable gate voltage above the supply voltage threshold
3Use of energy by stationary object
If larger resistor values are used to reduce power consumption, then power consumption decreases, but turn-on time increases
Solution Approach 1:
The pre-driven FET performs preliminary action by pre-charging the gate capacitance before the main FET turns on. This allows the use of larger resistor values for reduced power consumption while maintaining fast turn-on time, because the pre-charging reduces the voltage swing required during the main turn-on event
Solution Approach 2:
The patent employs periodic action through the pre-driven FET that operates in a distinct time window before the main FET switching. This temporal separation allows the pre-driven FET to prepare the gate voltage, enabling larger resistor values without compromising turn-on speed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The pre-driven bootstrapping gate driver circuit reduces the size and area of the bootstrap capacitors by up to 66.7%, while also improving the rise time and reducing power consumption.
Implementation Method 1
Bootstrapping gate drivers store energy in the form of charge in capacitors while an associated high side FET is turned off, and use the stored charge to apply a voltage greater than a supply voltage to the gate terminal of the high side FET
Implementation Method 2
The gate terminal and the drain terminal of FET 135 are shorted together, configuring FET 135 as a diode, and coupled to supply voltage Vdd
Data Source
AI summary
A bootstrapping gate driver circuit in which the size of the bootstrap capacitors is reduced. The gate-to-source voltage of the high side (pull-up) FET is pre-driven to an initial voltage (pre-driven voltage) before the bootstrap capacitor releases charge to charge up the gate-to-source voltage of the high side FET. This pre-driven voltage is applied through a pre-driven FET that allows current flow from the supply voltage to charge the gate of the high side FET to the pre-driven voltage. The pre-driven FET is turned on by a turn-on signal that occurs before the bootstrap capacitor releases charge. The pre-driven period (and hence, the pre-driven voltage) is determined from the time that the pre-driven FET begins to turn on, to the time that the bootstrap capacitor starts to release charge.