PTC From Microchip Simplifies Hands-Off Detection System Design

Microchip’s Peripheral Touch Controller solution makes it easy to quickly implement a low-power, high-sensitivity and environmentally robust HoD system.

Improve Vehicle Safety Using ADAS Technology

To improve safety, automotive original equipment manufacturers (OEMs) are increasing the number of advanced driver assistance systems (ADAS)in their vehicles. Ironically, some of these systems have inadvertently exposed occupants to higher danger levels instead of making their cars safer. For example, some drivers have misused lane-keeping assistance systems (LKAS) by removing their hands from the steering wheel when using automatic cruise control. While some drivers may have only wanted to test the limits of the systems, others may have misinterpreted the systems’ imitations, mistakenly believing that a “hands-off” operation is allowable under certain circumstances. Such behavior could have disastrous consequences if not addressed. As a result, the UN R79, which regulates LKAS, has been updated to require vehicles to monitor driver behavior and issue an alert if the driver removes their hands from the steering while LKAS is enabled, a feature commonly referred to as Hands-Off Detection (HoD).

HoD Design Considerations

HoD can be implemented in several ways, including torque, camera and capacitance sensing, each with advantages and disadvantages. Some important considerations when designing a HoD system include:

• Noise Immunity

This refers to a product’s immunity (ability to reject) unwanted voltages and currents, referred to as electrical noise. Higher noise immunity increases the reliability of a HoD system.

• Functional safety

ADAS systems improve the safety of vehicle occupants but can only achieve this if they are reliable. This requires them to implement one or more automatic protection functions to remove the unacceptable risk of injury or damage to people’s health. In addition, in-product functional safety mechanisms are used to detect, mitigate and correct faults caused by random errors when a system is in operation. ISO 26262is an international functional safety standard for electrical and electronic systems in road vehicles.

Microchip’s PTC Makes HoD Quick and Easy

Microchip’s Peripheral Touch Controller (PTC) solution makes it easy to quickly implement a low-power, high-sensitivity and environmentally robust HoD system (Figure 1).

Figure 1 Using Microchip technology to implement HoD

PTC is based on self-capacitance sensing with a driven shield and mutual capacitance, which both have excellent noise immunity performance. It also allows over-sampling and averaging by accumulating 1 to 64 samples. Furthermore, to reduce the effects of noise signals closer to the touch acquisition frequency, PTC supports frequency hopping using noise signal de-synchronization, providing high conducted immunity.

Microchip’s broad portfolio of functional safety-ready products includes microcontrollers (MCUs), digital signal controllers and interface and connectivity solutions recommended for design into the HoD system. Microchip’s AVR® DA family of microcontrollersbrings real-time control functionality and easy capacitive touch to the low-power performance of AVR MCUs. It pairs the latest Core Independent Peripherals (CIPs) with a robust integrated analog portfolio to create a device that excels as a stand-alone processor and as a companion MCU in designs that demand precision. The ASIL-B-ready AVR-DA series (certified by SGS-TUV) can be included in a HoD system alongside our functional safety-ready ATA663454LIN transceiver, which integrates a 5V regulator, a high-side switch and a watchdog which can be used to monitor the central controller for functional safety. Failure Modes Effects and Diagnostic Analysis (FMEDA) is used as a tool to identify the portions of an integrated circuit (IC) that are not safety-relevant and to assign diagnostics to detect failures in the part of the die that is safety-relevant. This results in a much lower residual failure in time (FIT) rate. Microchip provides the FMEDA and safety manuals to implement a reliable HoD system. In addition to functional safety components, we offer a broad portfolio of safety compilers and software.

Summary

Addressing sensor design, EMC/EMI concerns and functional safety in an HoD system is complex. However, our rich experience in HoD systems allows us to provide a low-cost, easy and quick solution which can help you achieve mass production of reliable products quickly.

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