Hands-Off Detection IC Enhances ADAS Safety
What you’ll learn:
- The RAA2S4704 IC offers HMI and hands‑off detection (HOD) capabilities.
- Capacitance and conductance information is derived from measured impedance.
Introducing a potentially game-advancing component is a bit like a golfer hitting a hole in one. Both events happen relatively infrequently, yet everyone knows there’s another one coming but not exactly when or by whom. So, under the category “look what we have here” is the appearance of a new member of Renesas’s family of mixed-signal sensor ICs that measure impedance.
The RAA2S4704 IC offers human-machine interface (HMI) and hands‑off detection (HOD) capabilities, crucial for ensuring driver safety in vehicles with advanced driver-assistance systems (ADAS).
It derives capacitance and conductance information from measured impedance, providing accurate assessments across a wide frequency range. Such flexibility enables the measurement of both in-phase and quadrature sensor components, which describes their relationships with the amplitude- and phase-modulated carrier.
The Importance of HOD in Automated Driving
This part is a critical element of a system designed to monitor whether a driver's hands are on the steering wheel, especially when ADAS or semi-autonomous driving features are engaged. It enables regulatory compliance for features like lane keeping assist systems (LKAS), support for safe transitions between manual and automated driving, and gesture controls (replaces switches—blinkers, A/C, volume, etc.—with single/multiple tapping or sliding gestures).
The hands-on/hands-off detection function makes it possible to know who is in control of a vehicle, and at which precise moment. HOD ensures drivers remain engaged when ADAS features are activated by monitoring the driver's interaction with the steering wheel. It continuously tracks changes in electrical impedance levels through sensors in the steering wheel, providing real-time feedback to determine if the driver's hands are on the wheel.
A “hands off” detection warning is required by the UN R79 regulation for LKAS. The UN R157 regulation covering automated lane keeping systems (ALKS) requires “hands on” detection as a key condition for the transition from automated back to manual driving mode.
Features of the RAA2S4704
The RAA2S4704 is said to provide superior accuracy and reliability compared to existing capacitive‑only measurement methods, simplifying system design and reducing costs by minimizing the need for external components. Target applications for the new device include automotive HOD, ADAS/AD, and capacitive sensing and impedance measurement.
The RAA2S4704’s electromagnetic compliance is tested according to IEC 161967-4 (conducted emission), IEC 62132-4 (conducted immunity), and IEC 61967-8 (radiated emission) standards. All sensor inputs are short-circuit protected and can handle overvoltage up to 18 V for SIO (separate input/output) pins (Renesas provides absolute maximum ratings).
As for other features and benefits, they include:
- Increased ability to detect scenarios with little capacitive change:
- System sensitivity of up to 5 fF/LSB
- Measurement update rate of 500 µs
- Can be used in combination with steering wheel heaters.
- Development process compliant with ISO 26262 ASIL B.
- Two external temperature sensors.
- Wide power supply (3.3 to 5 V).
- Up to 16 flexible adjustable measurement schemes.
- AEC-Q100 qualified QFN24 package (4 × 4 mm)
The RAA2S4704 has an evaluation board providing programming, simulation, and testing functions for the multichannel impedance measurement IC, supporting up to seven channels. The evaluation kit package includes the hardware, Renesas IC Toolbox (RICBox), and the RAA2S4704 plug-in.