Trickle Charge Control Circuit for Motor Drivers
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Solution Overview
Problem
Conventional solutions for providing adequate gate voltage to high-side MOSFETs in motor driver circuits require dedicated charge pumps for each circuit, leading to increased space and power consumption, especially in multi-phase motors where bootstrap capacitors may discharge during low-frequency operation.
Innovation Solution
A trickle charge control circuit is introduced to sense the voltage at the bootstrap capacitor node and dynamically couple or decouple a charge pump voltage to the motor driver circuit, ensuring the bootstrap capacitor remains charged only when the voltage at the bootstrap capacitor is greater than the input voltage, allowing a single charge pump to serve multiple motor driver circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated charge pump is provided for each motor driver circuit, then adequate gate voltage is ensured for high-side MOSFETs, but the required area and power consumption increase
Solution Approach 1:
A single charge pump is designed to serve multiple motor driver circuits by dynamically enabling or disabling its output to specific circuits based on their bootstrap capacitor voltage levels. The charge pump circuit is configured to provide trickle charge to any motor driver circuit that requires it, replacing the conventional approach of having dedicated charge pumps for each circuit.
Solution Approach 2:
A control circuit acts as an intermediary between the single charge pump and multiple motor driver circuits. This control circuit monitors the voltage at the bootstrap capacitor voltage node (VBST) of each motor driver circuit and dynamically couples or decouples the charge pump output to the appropriate circuit, enabling intelligent resource allocation.
2Reliability
If a dedicated charge pump is provided for each motor driver circuit, then bootstrap capacitors remain charged during low-frequency operation, but power consumption increases
Solution Approach 1:
The charge pump system transitions from a static dedicated configuration to a dynamic shared configuration. The control circuit continuously monitors bootstrap capacitor voltage levels and dynamically enables or disables the charge pump connection to specific motor driver circuits based on real-time voltage conditions, allowing the system to adapt to varying operational demands.
Solution Approach 2:
Each motor driver circuit monitors its own bootstrap capacitor voltage level and signals when it needs charging. The single charge pump responds to these individual needs, providing trickle charge only to circuits that require it, rather than continuously powering all circuits regardless of their actual charge status.
3Reliability
If the charge pump is continuously coupled to the motor driver circuit, then the bootstrap capacitor remains charged, but the voltage at VBST may exceed the voltage at VIN causing improper MOSFET operation
Solution Approach 1:
The control circuit implements voltage feedback by continuously monitoring the voltage at the bootstrap capacitor voltage node (VBST) and comparing it to the input voltage (VIN). Based on this feedback, the control circuit dynamically adjusts the coupling between the charge pump and the motor driver circuit, enabling the charge pump only when VBST is below VIN and disabling it when VBST exceeds VIN, thus preventing improper MOSFET operation.
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
This approach reduces the required area by allowing a single charge pump to provide trickle charging for multiple motor driver circuits, preventing premature discharge of bootstrap capacitors during low-frequency operation and maintaining adequate gate voltage for the high-side MOSFETs.
Implementation Method 1
a charge pump coupled to VIN and configured to generate a voltage at a charge pump voltage node (VCP), where a voltage at VCP is greater than a voltage at VIN
Implementation Method 2
a bootstrap capacitor coupled between a bootstrap capacitor voltage node (VBST) and VSW
Implementation Method 3
The trickle charge control circuit is configured to sense a voltage at a bootstrap capacitor voltage node (VBST) of the motor driver circuit; as a result of the voltage at VBST being greater than a voltage at an input voltage node (VIN), couple a charge pump voltage node (VCP) to VBST
Data Source
AI summary
A system includes a trickle charge control circuit coupled to a charge pump and a motor driver circuit. The trickle charge control circuit is configured to sense a voltage at a bootstrap capacitor voltage node (VBST) of the motor driver circuit; as a result of the voltage at VBST being greater than a voltage at an input voltage node (VIN), couple a charge pump voltage node (VCP) to VBST of the motor driver circuit, where a voltage at VCP is greater than the voltage at VIN; and as a result of the voltage at VBST being less than the voltage at VIN, decouple VCP from the charge pump from VBST of the motor driver circuit.