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AS5245

Data Sheet - D e t a i l e d D e s c r i p t i o n

8 Detailed Description

The AS5245 is manufactured in a CMOS standard process and uses a spinning current Hall technology for sensing the magnetic field

distribution across the surface of the chip. The integrated Hall elements are placed around the center of the device and deliver a voltage

representation of the magnetic field at the surface of the IC.

Through Sigma-Delta Analog / Digital Conversion and Digital Signal-Processing (DSP) algorithms, the AS5245 provides accurate high-resolution

absolute angular position information. For this purpose, a Coordinate Rotation Digital Computer (CORDIC) calculates the angle and the

magnitude of the Hall array signals. The DSP is also used to provide digital information at the outputs MagINCn and MagDECn that indicate

movements of the used magnet towards or away from the device’s surface. A small low cost diametrically magnetized (two-pole) standard

magnet provides the angular position information (see Figure 16).

The AS5245 senses the orientation of the magnetic field and calculates a 12-bit binary code. This code can be accessed via. a Synchronous

Serial Interface (SSI). In addition, an absolute angular representation is given by a Pulse Width Modulated signal at pin 12 (PWM). This PWM

signal output also allows the generation of a direct proportional analog voltage, by using an external Low-Pass-Filter. The AS5245 is tolerant to

magnet misalignment and magnetic stray fields due to differential measurement technique and Hall sensor conditioning circuitry.

Figure 4. Typical Arrangement of AS5245 and Magnet

8.1 Mode_Index Pin

The Mode_Index pin activates or deactivates an internal filter that is used to reduce the analog output noise. Activating the filter (Mode pin =

LOW or open) provides a reduced output noise of 0.03º rms. At the same time, the output delay is increased to 384µs. This mode is

recommended for high precision, low speed applications.

Deactivating the filter (Mode pin = HIGH) reduces the output delay to 96µs and provides an output noise of 0.06º rms. This mode is

recommended for higher speed applications.

Setting up the Mode pin affects the following parameters:

Note:

A change of the Mode during operation is not allowed. The setup must be constant during power up and during operation.

Table 6. Slow and Fast Mode Parameters

Parameter

Slow Mode (mode=low or open)

Sampling rate

2.61 kHz (384 µs)

10.42 kHz (96µs)

Transition noise (1 sigma)

≤ 0.03º rms

≤ 0.06º rms

Output delay

384µs

96µs

Maximum speed @ 4096 samples/rev

38 rpm

153 rpm

Maximum speed @ 1024 samples/rev

153 rpm

610 rpm

Maximum speed @ 256 samples/rev

610 rpm

2441 rpm

Maximum speed @ 64 samples/rev

2441 rpm

9766 rpm