Application of Hall sensor and current ripple technology in electric window anti-pinch

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Application of Hall sensor and current ripple technology in electric window anti-pinch [Copy link]

Author: Ivy Jin

With the continuous development of modern automobile technology, people are pursuing a more comfortable and easy-to-operate driving environment. Therefore, more and more cars are equipped with electric windows to achieve automatic lifting of windows. However, due to the fast rising speed of electric windows, it is easy to cause accidents such as pinching passengers, especially posing a safety hazard to children. This has put forward new standards for the safety of automobiles, requiring electric windows to have a certain anti-pinch function.

The anti-pinch function mainly means that when the window encounters an obstacle (such as a hand, head, etc.) during the rising process, it can identify that the window is in a clamped state and make it immediately stop rising and fall in the opposite direction, thereby avoiding accidents. It is an important manifestation of the humanization of the car.

This function has also been included in the legal regulations of many countries. The US Department of Transportation has issued the regulation FMVSSII8 for electric window systems, and the EU standard 74/60/EWG also clearly stipulates the anti-pinch force that the anti-pinch protection device should ensure. China has also issued similar regulations (GB 11552-2009), requiring that since 2012, the electric window lifts of new vehicles should have an anti-pinch function and the anti-pinch force should be less than 100N, that is, before the anti-pinch force reaches 100N, when the window glass opening is in the range of 4~200mm, the window should stop rising and fall in the opposite direction.

At present, the anti-pinch function of electric windows is mainly achieved through the following two solutions: Hall sensor solution and sensorless solution based on ripple counting.

1. Hall sensor solution

This solution installs a magnetic ring on the motor shaft and a Hall sensor near the magnetic ring. When the motor rotates, it drives the magnetic ring to rotate, and high and low level pulse signals are sensed on the Hall sensor. The number of pulses reflects the position of the motor, and the frequency of the pulses reflects the speed of the motor.

When the electric window rises and encounters an obstacle, the resistance becomes greater, the motor speed will slow down, and the pulse width of the corresponding pulse signal will become larger. At this time, the system will report information to the ECU module, and the ECU will send a command to the relay or motor driver chip to stop or reverse the motor, thereby stopping or lowering the window to achieve anti-pinch judgment.

The DRV5013-Q1 is a bipolar Hall-effect sensor with a wide operating voltage range (2.7 to 38 V) and reverse polarity protection up to -22 V, making it suitable for a wide range of automotive applications. In addition, the device also has internal protection features such as load dump, output short circuit and overcurrent.

Figure 1 Field direction definition of DRV5013-Q1	Figure 2 DRV5013-Q1 output

This solution requires the installation of a magnetic ring and each window requires its own controller, so the cost is relatively high.

Compared with the Hall sensor solution, the sensorless solution based on ripple counting can save the cost of magnetic rings, Hall sensors and related wiring harnesses. In addition, this solution can use a single controller to control multiple windows at the same time, which can improve the integration of the whole vehicle and further reduce the cost of the controller. Therefore, the sensorless solution based on ripple counting will become the development trend of electric window anti-pinch in the future.

2. Sensorless solution based on ripple counting

The sensorless solution of ripple counting utilizes the current ripple generated by the brushes switching between poles during the rotation of the rotor, and samples, analyzes and controls this current fluctuation.

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Figure 3 DC motor

This solution first converts the motor current signal into a voltage signal through a sampling resistor, and then filters and amplifies the voltage signal through an op amp. The amplified signal is converted into a digital signal through AD and sent to the MCU as a basis for judging anti-pinch and stall. The other way is to get a square wave signal through a filter and a comparator. The frequency of this square wave is proportional to the speed of the motor. The position and speed of the motor can be judged by the number and frequency of the square wave.

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Figure 4 System block diagram of TIDA-01421

The reference design TIDA-01421 provides a sensorless ripple anti-pinch solution. The design is mainly divided into the following parts:

• Current Sense Amplifier

The INA240-Q1 is a wide common-mode range, high-precision, bidirectional current sense amplifier. The device has a common-mode range of –4V to 80V and a large common-mode rejection ratio of 120dB, providing accurate, low-noise measurements.

A simple RC input filter can be used at the input of the INA240-Q1 in the application to reduce noise generated by high-frequency motor brushes and potential PWM switching noise.

• Bandpass filter

The output of the current sense amplifier is filtered through an active bandpass filter to remove additional noise and DC components, resulting in a current ripple signal.

The TLV2316-Q1 is a dual-channel, low-voltage, rail-to-rail general-purpose operational amplifier. The device features integrated RFI and EMI suppression filters that are unity-gain stable, will not experience phase reversal under overdrive conditions, and has high electrostatic discharge (ESD) protection (4kV HBM).

• Differential Amplifier

When a motor starts, there is a very large initial spike in the motor current, known as the inrush current. This current spike is large enough and slow enough that it cannot be filtered out by the high-pass circuit. With a differential amplifier, this slow, high-amplitude current spike can be removed from the signal, generating a low-noise AC signal for the next comparator stage to measure.

• Comparator

The signal output by the differential amplifier is finally generated by the comparator as a 0V to 3.3V square wave signal, whose frequency is equal to the motor current ripple frequency. This square wave signal is finally supplied to the MCU for counting.

The LMV7275-Q1 is a rail-to-rail input, low-power comparator with an open-drain output. The small SC-70 package is ideal for low-voltage, low-power, space-constrained designs.

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Figure 5 Output waveforms at each level

In summary, this article introduces the basic principles of two solutions for electric window anti-pinch technology - Hall sensor and ripple anti-pinch technology, and compares the advantages of ripple solution over Hall in practical applications. Although the Hall solution occupies a dominant position in the current market for window anti-pinch applications with its mature technology and high reliability, with the continuous development of mechanical processing technology and electronic technology, the increasing trend of ripple technology market share will become more and more obvious.