This article discusses a magnetic encoder intended for electrical motor driving employing ATS605LSG. It includes the advantages of magnetic encoder, guidelines for motor driving, general applications requirements, the ATS605LSG dual differential high-speed sensor, parameters definition when designing the target, analysis of phase separation and duty cycle, air gap influence, target pitch and teeth height recommendations, max air gap, phase variation, and optimized number of teeth for various target diameters.
Introduction
Encoders are normally used in electrical motor control systems to synchronize the excitation signals. This application note describes how to use a Hall sensor device such as the Allegro ATS605LSG as an encoder in a system with a ferrous target, and gives target design recommendations to achieve outputs in quadrature and a 50% duty cycle for each output.
Advantages of Magnetic Encoder
When designing a system with an electrical motor, the feedback loop is crucial to provide accurate excitation to the motor and increase its efficiency. An electrical motor system is often subject to more than electrical constraints; the size and the magnetic environment can also impact the overall performances. The advantages provided by a magnetic encoder such as the ATS605LSG include:
Immunity to external field
Simple construction
Ferrous target use
Automotive compliance
System size
Design freedom
Guidelines for Motor Driving
The encoder provide two signals in quadrature of phase, called CHA and CHB (Figure 2). These signals are used to provide the required feedback to the controller and adjust the motor excitation signals.
General Application Requirements
The designof the mechanical target can vary for each application. However, some parameters can be defined as general requirements for encoder systems and will be consistent for the majority of applications:
Duty cycle accuracy 50%
±10%
Phase shift accuracy 90° ±10°
Air gap from 0.5 to 3.0 mm
Temperature range –40°C to 150°C
The guidelines provided in this document focus on achieving these parameters.
If different parameters are required, this will impact the target design – contact a local Allegro application engineer to optimize the target design.
