Hall-effect angle sensor ICs for motor positioning

7th July 2015
Nat Bowers

Designed for high-speed motor position sensing in safety-critical automotive applications, the A1331 and A1334 contactless, Hall-effect based magnetic sensor ICs have been announced by Allegro MicroSystems Europe. The dual-die devices are based on vertical Hall-effect technology with system-on-chip architecture that provides fast output refresh rates and low signal path latency.

Each device is offered in a TSSOP-24 package that contains two individually sawn, electrically isolated silicon ICs. The dual-die feature makes them suitable for use in safety-critical applications that require the use of redundant sensor ICs, especially in ASIL compliant automotive systems. The A1334 is also offered in a single die configuration in the TSSOP-14 package for applications that do not require redundancy.

Typical applications include electronic power steering or power braking motor position sensing, transmission actuator position sensing, throttle/pedal position detection, and other systems that require accurate measurement of angular or rotary position.

The A1331 and A1334, with their onboard digital signal processing functions and EEPROM for factory and customer programmability, are designed specifically for on-axis/end-of-shaft angle sensing applications that require ultra-fast output refresh rates and low signal path latency.

These sensor ICs include a 4-wire 10MHz SPI interface with a 25µs output refresh rate and a nominal signal path latency of only 60µs. In addition, the ICs can operate directly off a vehicle battery, supporting a wide 4.5-14.5V supply voltage range while consuming just 10mA (maximum) of supply current per silicon die. They also include signal path and I/O diagnostics designed to meet the stringent needs of ASIL safety requirements.

Both devices can operate in a low RPM mode, to support up to 12-bit output resolution, and in a high RPM mode, to support situations demanding faster refresh rates and lower single path latency. As part of their signal processing functions, the ICs include automotive-grade temperature compensation to provide accurate angle measurements over the full operating temperature (from -40 to +150°C) and voltage (4.5-14.5 V) ranges of the devices.

The A1331 and A1334 output signals maintain a high level of accuracy over a wide magnetic field range, and can operate over a field range from less than 300 to greater than 1000G. On-chip EEPROM technology also enables flexible customer programming of the ICs.

The A1331 IC is unique in that it contains both a micropower mode of operation and an internal electronic turns counter function. Both of these features are important in electronic power steering applications, where it is important to keep track of the absolute position of the steering wheel over multiple revolutions. The A1331 can be connected to the vehicle battery, and placed into micropower mode (100µA average consumption per die) when the automobile is in the key-off state.

The A1331 will detect turning of the steering wheel while in micro-power mode and will sense and store the revolution count of the steering wheel, even while the car is in the key-off position. As a result, when the vehicle is powered up (key-on position), the steering system is aware of the absolute position of the steering wheel. This turns counter function counts in increments of 180 mechanical degrees, with a range of 511 positive increments and 512 negative increments.

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