AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
Revision 1.0, 11-Jan-06
www.austriamicrosystems.com
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1
General Description
The AS5045 is a contactless magnetic rotary encoder for
accurate angular measurement over a full turn of 360.
It is a system-on-chip, combining integrated Hall
elements, analog front end and digital signal processing
in a single device.
To measure the angle, only a simple two-pole magnet,
rotating over the center of the chip, is required. The
magnet may be placed above or below the IC.
The absolute angle measurement provides instant
indication of the magnet's angular position with a
resolution of 0.0879 = 4096 positions per revolution.
This digital data is available as a serial bit stream and as
a PWM signal.
An internal voltage regulator allows the AS5045 to
operate at either 3.3 V or 5 V supplies
Figure 1: Typical arrangement of AS5045 and magnet
1.1
Benefits
-
Complete system-on-chip
-
Flexible system solution provides absolute and PWM
outputs simultaneously
-
Ideal for applications in harsh environments due to
contactless position sensing
-
No calibration required
1.2
Key Features
-
Contactless high resolution rotational position
encoding over a full turn of 360 degrees
-
Two digital 12bit absolute outputs:
- Serial interface and
- Pulse width modulated (PWM) output
-
User programmable zero position
-
Failure detection mode for magnet placement
monitoring and loss of power supply
-
"red-yellow-green" indicators display placement of
magnet in Z-axis
-
Serial read-out of multiple interconnected AS5045
devices using Daisy Chain mode
-
Tolerant to magnet misalignment and airgap
variations
-
Wide temperature range: - 40C to + 125C
-
Small Pb-free package: SSOP 16 (5.3mm x 6.2mm)
1.3
Applications
-
Industrial applications:
- Contactless rotary position sensing
- Robotics
-
Automotive applications:
- Steering wheel position sensing
- Transmission gearbox encoder
- Headlight position control
- Torque sensing
- Valve position sensing
-
Replacement of high end potentiometers
This product is covered by one or more pending European and U.S. patents
DATA SHEET
AS5045
12 BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
Revision 1.0, 11-Jan-06
www.austriamicrosystems.com
Page 2 of 24
2
Pin Configuration
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
MagINCn
MagDECn
NC
NC
NC
Mode
VSS
Prog_DI
DO
CLK
CSn
PWM
NC
NC
VDD3V3
VDD5V
AS5045
Figure 2: Pin configuration SSOP16
2.1
Pin Description
Table 1 shows the description of each pin of the standard
SSOP16 package (Shrink Small Outline Package, 16
leads, body size: 5.3mm x 6.2mmm; see Figure 2).
Pins 7, 15 and 16 are supply pins, pins 3, 4, 5, 6, 13 and
14 are for internal use and must not be connected.
Pins 1 and 2 are the magnetic field change indicators,
MagINCn and MagDECn (magnetic field strength
increase or decrease through variation of the distance
between the magnet and the device). These outputs can
be used to detect the valid magnetic field range.
Furthermore those indicators can also be used for
contact-less push-button functionality.
Pin 6 Mode allows switching between filtered (slow) and
unfiltered (fast mode). See section 4
Pin Symbol
Type
Description
1
MagINCn
DO_OD
Magnet Field Magnitude INCrease;
active low, indicates a distance
reduction between the magnet and
the device surface. See Table 5
2 MagDECn DO_OD
Magnet Field Magnitude DECrease;
active low, indicates a distance
increase between the device and the
magnet. See Table 5
3
NC
-
Must be left unconnected
4
NC
-
Must be left unconnected
5
NC
-
Must be left unconnected
6 Mode
-
Select between slow (open, low:
VSS) and fast (high) mode. Internal
pull-down resistor.
7
VSS
S
Negative Supply Voltage (GND)
8 Prog_DI DI_PD
OTP Programming Input and Data
Input for Daisy Chain mode. Internal
pull-down resistor (~74k
).
Connect to VSS if not used
9 DO
DO_T Data Output of
Synchronous Serial Interface
Pin Symbol
Type
Description
10 CLK
DI,
ST
Clock Input of
Synchronous Serial Interface;
Schmitt-Trigger input
11 CSn
DI_PU,
ST
Chip Select, active low; Schmitt-
Trigger input, internal pull-up resistor
(~50k
)
12 PWM
DO
Pulse Width Modulation of approx.
1kHz; LSB in Mode3.x
13
NC
-
Must be left unconnected
14
NC
-
Must be left unconnected
15 VDD3V3 S
3V-Regulator Output, internally
regulated from VDD5V. Connect to
VDD5V for 3V supply voltage. Do not
load externally.
16
VDD5V
S
Positive Supply Voltage, 3.0 to 5.5 V
Table 1: Pin description SSOP16
DO_OD
digital output open drain
S
supply pin
DO
digital output
DI
digital input
DI_PD
digital input pull-down
DO_T digital output /tri-state
DI_PU
digital input pull-up
ST
Schmitt-Trigger input
Pin 8 (Prog) is used to program the zero-position into the
OTP (see chapter 8.1).
This pin is also used as digital input to shift serial data
through the device in Daisy Chain configuration,
(see page 6).
Pin 11 Chip Select (CSn; active low) selects a device
within a network of AS5045 encoders and initiates serial
data transfer. A logic high at CSn puts the data output
pin (DO) to tri-state and terminates serial data transfer.
This pin is also used for alignment mode (Figure 12) and
programming mode (Figure 9).
Pin 12 allows a single wire output of the 10-bit absolute
position value. The value is encoded into a pulse width
modulated signal with 1s pulse width per step (1s to
4096s over a full turn). By using an external low pass
filter, the digital PWM signal is converted into an analog
voltage, making a direct replacement of potentiometers
possible.
3
Functional Description
The AS5045 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 AS5045
provides accurate high-resolution absolute angular
AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
Revision 1.0, 11-Jan-06
www.austriamicrosystems.com
Page 3 of 24
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 MagI NCn and M agDECn 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 15).
The AS5045 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 analogue voltage, by using an external Low-
Pass-Filter.
The AS5045 is tolerant to magnet misalignment and
magnetic stray fields due to differential measurement
technique and Hall sensor conditioning circuitry.
Figure 3: AS5045 block diagram
4
Mode Input Pin
The mode input 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 0.03 rms. At the same time, the output
delay is increased to 384s. This mode is recommended for high precision, low speed applications.
Deactivating the filter (Mode pin = HIGH) reduces the output delay to 96s and provides an output noise of 0.06 rms. This
mode is recommended for higher speed applications.
Switching the Mode pin affects the following parameters:
Parameter
slow mode (Mode = low or open)
fast mode (Mode = high, VDD5V)
sampling rate
2.61 kHz (384 s)
10.42 kHz (96s)
transition noise (1 sigma)
0.03 rms
0.06 rms
output delay
384s
96s
max. speed @ 4096 samples/sec.
max. speed @ 1024 samples/sec.
max. speed @ 256 samples/sec.
38 rpm
153 rpm
610 rpm
153 rpm
610 rpm
2442 rpm
Table 2: Slow and fast mode parameters
AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
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5
12-bit Absolute Angular Position Output
5.1
Synchronous Serial Interface (SSI)
D11
1
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
OCF COF
LIN
Mag
INC
Mag
DEC
Even
PAR
D11
1
18
8
t
CLK FE
t
CSn
t
DO Tristate
Status Bits
Angular Position Data
t
DO valid
t
DO active
T
CLK/2
t
CLK FE
CSn
DO
CLK
Figure 4: Synchronous serial interface with absolute angular position data
If CSn changes to logic low, Data Out (DO) will change from
high impedance (tri-state) to logic high and the read-out will
be initiated.
After a minimum time t
CLK FE,
data is latched into the
output shift register with the first falling edge of CLK.
Each subsequent rising CLK edge shifts out one bit of
data.
The serial word contains 18 bits, the first 12 bits are
the angular information D[11:0], the subsequent 6 bits
contain system information, about the validity of data
such as OCF, COF, LIN, Parity and Magnetic Field
status (increase/decrease) .
A subsequent measurement is initiated by a "high"
pulse at CSn with a minimum duration of t
CSn.
5.1.1
Data Content
D11:D0 absolute angular position data (MSB is clocked
out first)
OCF (Offset Compensation Finished), logic high
indicates the finished Offset Compensation Algorithm
COF (Cordic Overflow), logic high indicates an out of
range error in the CORDIC part. When this bit is set, the
data at D9:D0 is invalid. The absolute output maintains
the last valid angular value.
This alarm may be resolved by bringing the magnet
within the X-Y-Z tolerance limits.
LIN (Linearity Alarm), logic high indicates that the input
field generates a critical output linearity.
When this bit is set, the data at D9:D0 may still be used,
but can contain invalid data. This warning may be
resolved by bringing the magnet within the X-Y-Z
tolerance limits.
Even Parity bit for transmission error detection of bits
1...17 (D11...D0, OCF, COF, LIN, MagINC, MagDEC)
Placing the magnet above the chip, angular values increase in clockwise direction by default.
Data D11:D0 is valid, when the status bits have the following configurations:
OCF COF LIN
Mag
INC
Mag
DEC
Parity
0 0
0 1
1 0
1 0 0
1*) 1*)
even
checksum of
bits 1:15
Table 3: Status bit outputs
*) MagInc=MagDec=1 is only recommended in YELLOW mode (see Table 5)
AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
Revision 1.0, 11-Jan-06
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5.1.2
Z-axis Range Indication (Push Button Feature, Red/Yellow/Green Indicator)
The AS5045 provides several options of detecting
movement and distance of the magnet in the Z-direction.
Signal indicators MagINCn and MagDECn are available both
as hardware pins (pins #1 and 2) and as status bits in the
serial data stream (see Figure 4). Additionally, an OTP
programming option is available with bit MagCompEn (see
Figure 9) that enables additional features:
In the default state, the status bits MagINC, MagDec
and pins MagINCn, MagDECn have the following function:
Status bits
Hardware pins
OTP: Mag CompEn = 0 (default)
Mag
INC
Mag
DEC
Mag
INCn
Mag
DECn
Description
0 0 Off Off
No distance change
Magnetic input field OK (in range, ~45...75mT)
0 1 Off On
Distance increase; pull-function. This state is dynamic and only active while the magnet is
moving away from the chip.
1 0 On Off
Distance decrease; push- function. This state is dynamic and only active while the magnet is
moving towards the chip.
1 1 On On
Magnetic input field invalid out of recommended range:
too large, too small (missing magnet)
Table 4: Magnetic field strength variation indicator
When bit MagCompEn is programmed in the OTP, the function of status bits MagINC, MagDec
and pins MagINCn, MagDECn is changed to the following function:
Status bits
Hardware pins
OTP: Mag CompEn = 1 (red-yellow-green programming option)
Mag
INC
Mag
DEC
LIN
Mag
INCn
Mag
DECn
Description
0 0 0 Off Off
No distance change
Magnetic input field OK ( GREEN range, ~45...75mT)
1 1 0 On Off
YELLOW range: magnetic field is ~ 25...45mT or ~75...135mT. The AS5045 may
still be operated in this range, but with slightly reduced accuracy.
1 1 1 On On
RED range: magnetic field is ~<25mT or >~135mT. It is still possible to operate the
AS5045 in the red range, but not recommended.
All other combinations
n/a
n/a
Not available
Table 5: Magnetic field strength red-yellow-green indicator (OTP option)
Note: Pin 1 (MagINCn) and pin 2 (MagDECn) are active low via open drain output and require an external pull-up resistor. If
the magnetic field is in range, both outputs are turned off.
The two pins may also be combined with a single pull-up resistor. In this case, the signal is high when the magnetic field is
in range. It is low in all other cases (see Table 5 and Table 5).
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