as5304 austriamicrosystems, as5304 Datasheet - Page 7

• Manufacturer Part Number: as5304
• Description: Integrated Hall Ics For Linear And Off-axis Rotary Motion Detection
• Manufacturer: austriamicrosystems

AS5304/AS5306 Integrated Hall IC for linear and off-axis rotary motion detection
8
The Analog Output (AO) provides an analog output voltage that represents the Automatic Gain Control (AGC) of the Hall
sensors signal control loop.
This voltage can be used to monitor the magnetic field strength and hence the gap between magnet and chip surface:
For ideal operation, the AO voltage should be between 1.0 and 4.0V.
8.1
When using the AS5304/06 in an off-axis rotary application, a multi-pole ring magnet must be used. Resolution, diameter and
maximum speed depend on the number of pole pairs on the ring.
8.1.1
The angular resolution increases linearly with the number of pole pairs. One pole pair has a resolution (= interpolation factor) of
160 steps or 40 quadrature pulses.
Resolution [steps] = [interpolation factor] x [number of pole pairs]
Resolution [bit] = log (resolution[steps]) / log (2)
Revision 1.0
•
•
The AO output
Resolution and maximum rotating speed
Example: multi-pole ring with 22 pole pairs
Resolution
Short distance between magnet and IC → strong magnetic field → low loop gain → low AO voltage
Long distance between magnet and IC → weak magnetic field → high loop gain → high AO voltage
Resolution
= 160x22 = 3520 steps per revolution
= 40x22 = 880 quadrature pulses / revolution
= 11.78 bits per revolution = 0.1023° per step
Figure 9: AO output versus AGC, magnetic field strength, magnet-to-IC gap
5
4
3
2
1
A O
[V]
strong field,
S m all gap,
R ecom m ended
low AGC
range
www.austriamicrosystems.com
Large gap,
weak field,
high AGC
Page 7 of 12