Analog Devices Inc. ADMT4000 True Power-On Multi-Turn Position Sensor

The Analog Devices ADMT4000 is a magnetic sensor designed to record the number of rotations of a magnetic system. A key feature of this device is its ability to retain the rotational count even during periods of power interruption. Upon subsequent power-up, the absolute position of the magnetic system can be retrieved, including the number of turns. The sensor transmits digital output via the Serial-Peripheral Interface (SPI). The ADMT4000 is capable of counting up to 46 rotations of an external magnetic field, with the absolute position value incrementing in a clockwise direction. This functionality enables the determination of precise positional information in multi-turn rotational applications. 

Flexible Features Suitable for High Accuracy and Smooth Data Acquisition

The ADMT4000 multi-turn position sensor incorporates a true power-on multiturn counter, enabling the precise tracking of rotational position across up to 46 complete revolutions of a magnetic system. The sensor employs magnetic field detection to measure the angular displacement, with a positive count accumulating in the clockwise direction starting from a magnetic reset point. 

The digital output provides a high resolution of more than 16,000 discrete steps over the full measurement range, facilitating fine positional control and feedback. Furthermore, it has an accuracy of ±0.25 degrees, ensuring reliable and precise angular measurements critical for demanding applications. The sensor is capable of a measurement update rate of 100,000 samples per second (SPS), allowing for the capture of rapidly changing positional information in dynamic systems.   

The operational magnetic field range is from 16 mT to 31 mT, providing flexibility in magnet selection and placement. Also, an integrated temperature sensor allows for on-chip temperature monitoring, which can be valuable for system diagnostics and environmental compensation. The device operates with a 3.3V integrated circuit supply voltage and supports an SPI with voltage levels ranging from 1.8V to 5V, ensuring compatibility with a wide array of digital control systems. The 24-pin Thin Shrink Small Outline Package (TSSOP) contributes to its compact form factor and facilitates integration into various mechanical assemblies

Multiple Types of Magnetic Sensing Elements for Changing Scenarios

The ADMT4000 incorporates three distinct magnetic sensing elements, each contributing to precise position determination and applicable in diverse scenarios. 

• The Giant Magneto Resistance (GMR) turn count sensor serves the fundamental purpose of tracking the total number of rotations executed by the magnetic system. This capability is crucial in applications where the number of complete revolutions is a significant parameter, such as in multi-turn actuators or rotary encoders requiring absolute position knowledge across a wide range of motion.

• The GMR quadrant detecting sensor complements the turn count sensor and an Anisotropic Magnetoresistive (AMR) angle sensor. 

• The AMR angle sensor, in conjunction with the GMR quadrant detecting sensor, provides high-resolution angular information within a single 360° rotation. This precise within-turn measurement is essential for applications demanding accurate positioning within a revolution, such as robotic joints or precision motor control. 

The combined operation of the GMR turn count sensor and the AMR angle sensor output enables the ADMT4000 to deliver a comprehensive absolute position reading with high angular accuracy over multiple rotations. This integrated approach is useful in applications like brushless DC motor control and positioning, where precise and absolute position feedback, accounting for both fractional turns and total rotations, is critical for optimal system performance and control.