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AAT003-10E

P1-P3P4-P6P7-P9P10-P12P13-P14
AAT003 Low-Resistance Angle Sensor
4
NVE Corporation 11409 Valley View Road, Eden Prairie, MN 55344-3617 Phone: (952) 829-9217 Fax: (952) 829-9189 www.nve.com ©NVE Corporation
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
024
48 72 96 120 144 168 192 216 240 264 288 312 336 360
Degrees of Rotation
V
oltage
Cosine, 3mm
Sine, 3mm
Cosine, 4mm
Sine, 4mm
Cosine, 5mm
Sine, 5mm
AAT-Series sensors are resistive devices with no active components, so they have no minimum voltage and can be powered from
single cells.
The following chart shows a typical sensor output versus the angle of applied field at different air gaps:
Figure 2. AAT003 Typical Output with Variations in Airgap
(5V supply; 12 mm diameter, 4 mm thick split-pole ferrite magnet; 5 V supply).
One cycle per revolution
Other sensor types such as AMR have two cycles per revolution, so they cannot determine absolute position for 360-degree
rotation. AAT-Series sensors output one cycle per revolution and can unambiguously determine position within a full rotation.
Detects absolute position
Unlike some encoder types, AAT-Series sensors detect absolute position, and maintain position information when power is
removed. The sensor immediately powers up indicating the correct position.
AAT003 Low-Resistance Angle Sensor
5
NVE Corporation 11409 Valley View Road, Eden Prairie, MN 55344-3617 Phone: (952) 829-9217 Fax: (952) 829-9189 www.nve.com ©NVE Corporation
Application Circuitry
External comparators
A dual comparator can provide digital outputs from AAT angle sensors. Low-power comparators and large resistors are used to
avoid adding power consumption to low-power applications:
2
1
34
6
5
R1 (Sine)
Sin
Vcc
GND
R2 (Sine)
R4 (Cosine)
R3 (Cosine)
Cos
Vcc
GND
100 nF
1M
1M
-
+
+
-
AAT00x Sensor
3.3 V
MCP
6542
360˚
0 90˚ 180˚ 270˚
Sgn(Cos)
Sgn(Sin)
Figure 2. External dual comparator for digital outputs.
Inherent comparator hysteresis eliminates noise at the transition points. The MCP6542 comparator hysteresis of 3.3 mV
corresponds to about 1 angular degree of hysteresis. Higher hysteresis comparators can be used for more noise immunity at the
expense of hysteresis.
NVE also offers ADT-Series sensors that include integrated comparators to replicate the circuit of Figure 2.
Quadrant outputs
A 2-to-4 line decoder can provide digital signals to indicate the quadrant of rotation:
2
1
34
6
5
R1 (Sine)
Sin
Vcc
GND
R2 (Sine)
R4 (Cosine)
R3 (Cosine)
Cos
Vcc
GND
100 nF
5M
5M
-
+
+
-
AAT00x Sensor
3.3 V
SN74LV
C1G139
A
B
MCP
6542
Y3
Y0
Y2
Y1
750
0˚-90˚
90˚-180˚
180˚-270˚
270˚-360˚
Figure 3. Digital Quadrant Outputs.
AAT003 Low-Resistance Angle Sensor
6
NVE Corporation 11409 Valley View Road, Eden Prairie, MN 55344-3617 Phone: (952) 829-9217 Fax: (952) 829-9189 www.nve.com ©NVE Corporation
Speed and direction signals
Commodity CMOS circuits can be added to create a precise encoder with direction and speed outputs. A flip-flop determines
direction by detecting the phasing between the two outputs. An exclusive-OR gate provides a digital signal with two cycles per
revolution, and transitions every 90 degrees:
2
1
34
6
5
R1 (Sine)
Sin
Vcc
GND
R2 (Sine)
R4 (Cosine)
R3 (Cosine)
Cos
Vcc
GND
100 nF
5M
5M
-
+
+
-
AAT00x Sensor
Speed
(2/rev)
7SZ86
3.3 V
SN74
AUP1G79
D
Q
CLK
Direction
TLV
3502
360˚270˚180˚
0
90˚
Figure 4. Speed and direction signals.
Rotation reference signals
An AAT angle sensor and a single comparator can provide a precise angular reference point and a one cycle-per-rotation signal.
Comparing the sine and cosine outputs is more precise than comparing either to a reference because it corrects for temperature.
AAT00x Sensor
2
1
34
6
5
R1 (Sine)
Sin
Vcc
GND
R2 (Sine)
R4 (Cosine)
R3 (Cosine)
Cos
Vcc
GND
-
+
100 nF
0.9 to 5.5 V
TLV3691
OUT
360˚
0
Sin
Cos
OUT
45˚
225˚
Figure 5. Angular Reference Point Rotation Signal.
In this circuit, the output is high from nominal 45 to 225 degrees, and low from 225 to 45 degrees. The TLV3691 comparator
hysteresis of 17 mV corresponds to approximately 6 degrees of hysteresis with a 1.5 V supply. A TS881 or similar comparator has
a typical hysteresis of 4 mV, corresponding to 1.5 angular degrees of hysteresis.
P1-P3P4-P6P7-P9P10-P12P13-P14

AAT003-10E

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