as5134 austriamicrosystems, as5134 Datasheet - Page 19

• Manufacturer Part Number: as5134
• Description: 360?programmable High Speed Bldc Magnetic Rotary Encoder
• Manufacturer: austriamicrosystems

AS5134
Data Sheet - D e t a i l e d D e s c r i p t i o n
The counter output can be reset by using command 20 – SET MT Counter. It is immediately reset by the rising clock
edge of this bit. Any zero crossing between the clock edge and the next counter readout changes the counter value.
High Speed Operation
The AS5134 is using a fast tracking ADC (TADC) to determine the angle of the magnet. The TADC is tracking the
angle of the magnet with cycle time of 4µs. Once the TADC is synchronized with the angle, it sets the LOCK bit in the
status register. In worst case, usually at start-up, the TADC requires up to 255 steps (255 * 4µS = 1020µs) to lock.
Once it is locked, it requires only one cycle (4µs) to track the moving magnet. The AS5134 can operate in locked mode
at rotational speeds up to min. 30,000 rpm.
In Low/Mid Power Mode, the position of the TADC is frozen. It will continue from the frozen position once it is powered
up again. If the magnet has moved during the power down phase, several cycles will be required before the TADC is
locked again. The tracking time to lock in with the new magnet angle can be roughly calculated as:
Where:
t
OldAngle = Angle position when one of the reduced power modes is activated [º]
NewAngle = Angle position after resuming from reduced power mode [º]
Propagation Delay
The Propagation delay is the time required from reading the magnetic field by the Hall sensors to calculating the angle
and making it available on the serial or PWM interface. While the propagation delay is usually negligible on low
speeds, it is an important parameter at high speeds. The longer the propagation delay, the larger becomes the angle
error for a rotating magnet as the magnet is moving while the angle is calculated. The position error increases linearly
with speed. The main factors that contribute to the propagation delay are discussed in detail further in this document.
ADC Sampling Rate
For high speed applications, fast ADC’s are essential. The ADC sampling rate directly influences the propagation
delay. The fast tracking ADC used in the AS5134 with a tracking rate of only 1.4 µs (typ) is a perfect fit for both high
speed and high performance.
Chip Internal Lowpass Filtering
A commonplace practice for systems using analog-to-digital converters is to filter the input signal by an anti-aliasing
filter. The filter characteristic must be chosen carefully to balance propagation delay and noise. The lowpass filter in the
AS5134 has a cutoff frequency of typ. 23.8kHz and the overall propagation delay in the analog signal path is typ.
15.6µs.
www.austriamicrosystems.com
LOCK
= Time required to acquire the new angle after power up from one of the reduced power modes [µs]
100000000
00000010
00000001
00000000
10000000
Bit Code
11111101
11111110
11111111
---
---
t
LOCK
=
------------------------------------------------------------------------- -
4μs ∗ NewAngle OldAngle
Revision 1.6
1.406
–
Decimal Value
-128
-255
+2
+1
---
---
-1
-2
-3
0
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(EQ 1)