Servo IC Sense FET Integration for Stable Current Control
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Solution Overview
Problem
Existing spindle motor control systems face challenges with large external sense resistors that occupy significant space, are costly, and have resistance variability, as well as complexity and accuracy issues due to multiple pins and FET variations, leading to instability in current sensing and control.
Innovation Solution
Integration of an external sense resistor into a servo IC with a stable resistance control circuit using a current mirror and transconductance amplifiers, allowing for programmable gain and synchronous change of sense transistor and resistor gain to maintain system stability and consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large external sense resistor is used to handle significant current, then current sensing capability is improved, but the resistor occupies significant real estate and increases cost
Solution Approach 1:
The patent merges the external sense resistor function into an integrated sense FET within the motor driver IC. The sense FET's channel resistance serves as the sensing element, eliminating the need for a separate external resistor. This integration combines multiple functions (current sensing, signal conditioning) into a single component, reducing external component count and PCB real estate while maintaining current sensing capability.
2Measurement precision
If a large external sense resistor is used to handle significant current, then current sensing capability is improved, but the resistor presents significant expense
Solution Approach 1:
The patent merges the external sense resistor function into an integrated sense FET within the motor driver IC. The sense FET's channel resistance serves as the sensing element, eliminating the need for a separate external resistor. This integration combines multiple functions (current sensing, signal conditioning) into a single component, reducing external component count and PCB real estate while maintaining current sensing capability.
3Measurement precision
If multiple pins are used for sensing (ICOM, RSNSP, RSNSN), then current sensing accuracy is improved by accounting for parasitic resistance, but device complexity increases
Solution Approach 1:
The patent merges the external sense resistor function into an integrated sense FET within the motor driver IC. The sense FET's channel resistance serves as the sensing element, eliminating the need for a separate external resistor. This integration combines multiple functions (current sensing, signal conditioning) into a single component, reducing external component count and PCB real estate while maintaining current sensing capability.
Solution Approach 2:
The patent introduces a current mirror as an intermediary element that replicates the current flowing through the sense FET and provides a scaled-down version for measurement. This current mirror allows accurate current sensing with fewer external pins by providing an isolated measurement path that doesn't require direct access to multiple high-current nodes.
4Ease of manufacture
If sense FETs are used for each phase, then current sensing is integrated, but FET variation requires trimming circuits that complicate the design
Solution Approach 1:
The patent introduces a current mirror as an intermediary element that replicates the current flowing through the sense FET and provides a scaled-down version for measurement. This current mirror allows accurate current sensing with fewer external pins by providing an isolated measurement path that doesn't require direct access to multiple high-current nodes.
Solution Approach 2:
The patent employs programmable gain amplifiers that can dynamically adjust their gain settings to compensate for process variations in the sense FET. By changing the electrical parameters (gain) of the amplifying circuits, the system can calibrate itself to account for FET variations without requiring physical trimming circuits, thus maintaining integration while reducing complexity.
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 solution reduces the need for external resistors, simplifies the circuit, and improves accuracy and stability in spindle motor control by maintaining consistent system gain during gain changes, enhancing the control loop's feedback and rotation speed management.
Implementation Method 1
a current mirror having the first sense FET and a mirror FET
Implementation Method 2
a first transconductance amplifier coupled to the first sense FET
Data Source
AI summary
An apparatus, comprises three driver FETs coupled at their sources; note-driver circuit; a first sense FET coupled to the sources of the three driver FETs; a current mirror having the first sense FET and a mirror FET; wherein the first sense FET is coupled to the mirror FET; a first transconductance amplifier coupled to the first sense FET; a second amplifier coupled to the current mirror, and an output of the first transconductance amplifier is an input to the second amplifier.