Bootstrap High-Side Switch Control for Negative Source Voltages
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Solution Overview
Problem
Existing pre-driver integrated circuits face challenges in managing negative voltages at the source node of high-side nMOS transistors, which can lead to transient currents and potential circuit damage, especially when dealing with complex loads containing significant inductive components.
Innovation Solution
A monolithic integrated circuit is designed to control high-side switching elements using a bootstrap capacitor, featuring a power supply control section with first and second switches, and comparators to manage power sources and prevent excessive charging or discharging of the bootstrap capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bootstrap capacitor is used to supply higher voltage to turn ON the nMOS transistor, then the transistor can be switched ON reliably, but negative voltage at the source node during switching causes transient currents that can damage the circuit
Solution Approach 1:
The patent introduces a pre-driver circuit as an intermediary between the control signal and the nMOS transistor gate. This pre-driver circuit actively manages the bootstrap capacitor charging and discharging, controlling the voltage transition at the gate to prevent excessive transient currents while ensuring reliable transistor switching.
Solution Approach 2:
The patent implements feedback control through the pre-driver circuit that monitors the source node voltage and adjusts the bootstrap capacitor charging/discharging accordingly. The circuit detects negative voltage conditions and modulates the charging current to prevent harmful transient effects while maintaining proper switching operation.
2Speed
If the slew rate of the source node voltage drop is increased to improve switching speed, then switching performance improves, but transient currents into or out of the bootstrap capacitor increase
Solution Approach 1:
The patent employs dynamic control of the bootstrap capacitor charging/discharging process through the pre-driver circuit. The circuit adjusts the charging rate and discharge timing based on the switching state and source node voltage, optimizing the slew rate to achieve fast switching while preventing excessive transient currents that would damage the circuit.
Solution Approach 2:
The patent utilizes periodic charging and discharging cycles of the bootstrap capacitor controlled by the pre-driver. The circuit rhythmically manages the capacitor state in synchronization with the switching requirements, ensuring that charging occurs at appropriate times and at controlled rates, thereby achieving fast switching without harmful transients.
3Ease of manufacture
If a discrete nMOS transistor is used instead of an integrated one, then lower ON-resistance and lower cost are achieved, but the complexity of managing negative source node voltages increases
Solution Approach 1:
The patent combines the pre-driver circuit and power supply control functionality into an integrated circuit that works with the discrete nMOS transistor. This integration consolidates the complexity of managing negative source node voltages and bootstrap capacitor control into a single coordinated system, maintaining the advantages of discrete transistors while reducing overall system complexity through unified control architecture.
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 solution effectively manages negative source node voltages, prevents transient currents, and maintains a clean pre-driver supply, thereby ensuring reliable operation of high-side switching elements and avoiding circuit damage.
Implementation Method 1
a bootstrap circuit which includes a bootstrap capacitor Cbs and an auxiliary voltage source stacked above a supply voltage source
Data Source
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AI summary
A monolithic integrated circuit (1) for controlling a high-side switching element (2) for a load (3) using a bootstrap capacitor is disclosed. The integrated circuit comprises a first supply voltage input (7) for receiving a first input supply voltage (V1), a second supply voltage input (8) for receiving a second, current-limited input supply voltage (VCP), a voltage-sensing input (14) for receiving a source voltage, a first output (15) for providing a drive signal (VG) to the switching element (2), a second output ( 16) for providing a charging signal (VBS) to a bootstrap capacitor (17), a pre-driver (18) for generating the drive signal, the pre-driver having a voltage input (20 ) and an output (22) which is coupled to the first output, and a power supply control section (25) comprising first and second switches (28,29). The first and second switches (28, 29) are arranged in series between the first input (7) and the second output ( 16), the second input ( 8 ) is coupled to a node (34) between the first and second switches (29), and the second node (34) is coupled to a voltage input (20 ) of the pre-driver. The first and second switches are selectively operable following switching of the switching element from an ON state to an OFF state and in response to a determination that the source voltage is below a predetermined level, to decouple the second output (16) and in response to determination that the source voltage is above the predetermined level to couple the second output (16) to the second output (16).