2012-06-25 New AS5132 rotary position sensor ensures accurate

New addition to ams’ line of magnetic sensor ICs ideal for use in brushless DC motor
control systems and other rotary position-sensing applications.

The AS5132 is a system-on-chip, combining integrated Hall elements, an analog front end and digital
signal processing in a single device. It is particularly well suited to industrial and automotive brushless
DC (BLDC) motors, where it offers designers a small, robust and easily assembled position sensing
solution. It is highly resistant to interference from stray magnetic fields.

The new device improves on previous generations of magnetic encoder by dynamically compensating
for angle errors attributable to propagation delay, which are most noticeable at high speeds. Error
compensation is achieved through integrated pre-commutation functions. These are very easy to configure in the AS5132, and do not require external software routines to be executed, therefore unburdening host microcontrollers or electronic control units (ECUs). The configuration can be changed while the device is operating, in response to changes in operating conditions such as variations in rotation speed.

In addition, the advanced signal-processing circuitry in the AS5132 gives it an excellent propagation
delay figure of <22μs, which means that even before pre-commutation is implemented the angle
error is small.
In combination, the small propagation delay and advanced pre-commutation deliver extremely accurate
angle measurement even in motors rotating at speeds up to 80,000rpm: angle measurements
are accurate to within ±3° (maximum). This enables BLDC motor manufacturers to achieve high and
constant levels of torque even in high-speed applications over the whole dynamic range.
Other improvements introduced in the AS5132 include:

  • increased sensitivity to allow operation in a magnetic field input as weak as 20mT. This enables the sensor to be paired with cheap ferrite magnet.
  • simplification of the interface for easier integration
  • inclusion of an external clock mode, synchronizing sensor and controller systems
  • implementation of a 3V interface mode (in addition to a 5V mode) eliminating the need for a lever shifter

When paired with a simple two-pole magnet, the AS5132 provides absolute angle measurement at
a resolution of 8.5 bits, or 360 positions per revolution. This measurement is available as a serial
output and as a pulse width modulated (PWM) signal.

An additional U,V,W output can be used for block commutation in a BLDC motor; alternatively an
incremental signal (ABI) is available. In addition to the angle information, the strength of the magnetic
field is represented as a 5-bit value.

The zero position can be set by software on the production line. This simplifies assembly, as the
magnet does not need to be precisely aligned with a fixed starting position.

The AS5132 is suitable for contactless rotary position sensing, rotary switches (human machine
interface), AC/DC motor position control and BLDC motor position control in automotive applications
such as pump BLDC motors (stop-start system) and steering column BLDC motors. The AS5132
is also particularly well suited to position sensing in double-clutch BLDC motors.

 

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