AS5134-ASSU austriamicrosystems, AS5134-ASSU Datasheet - Page 24

• Manufacturer Part Number: AS5134-ASSU
• Description: ENCODER, MAGNETIC, ROTARY, 8BIT, 20SSOP
• Manufacturer: austriamicrosystems

Specifications of AS5134-ASSU

• Brief Features: 9-Bit Multiturn Counter, User Programmable Zero Position And Sensitivity
• Supply Voltage Range: 4.5V To 5.5V
• Operating Temperature Range: -40°C To +140°C
• Digital Ic Case: RoHS Compliant
• Ic Function: Programmable High Speed Magnetic Rotary Encoder
• Rohs Compliant: Yes

AS5134
Data Sheet - D e t a i l e d D e s c r i p t i o n
In Low 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.
Digital Readout Rate
Aside from the chip-internal propagation delay, the time required to read and process the angle data must also be
considered. Due to its nature, a PWM signal is not very usable at high speeds, as you get only one reading per PWM
period. Increasing the PWM frequency may improve the situation but causes problems for the receiving controller to
resolve the PWM steps. The frequency on the AS5134 PWM output is typ. 1.33kHz with a resolution of 2µs/step. A
more suitable approach for high speed absolute angle measurement is using the serial interface. With a clock rate of
up to 6MHz, a complete set of data (21bits) can be read in >3.5µs.
Total Propagation Delay of the AS5134
The total propagation delay of the AS5134 is the delay in the analog signal path and the tracking rate of the ADC:
If only the SIN-/COS-outputs are used, the propagation delay is the analog signal path delay only (typ. 15.6µs).
Position Error Over Speed:
The angle error over speed caused by the propagation delay is calculated as:
In addition, the anti-aliasing filter causes an angle error calculated as:
Table 11. Examples of the Overall Position Error caused by Speed (includes both propagation delay and filter delay)
www.austriamicrosystems.com
LOCK
= Time required to acquire the new angle after power up from one of the reduced power modes [µs]
Speed (rpm)
10000
1000
100
t
LOCK
Δθ
pd
Δ
θ
= rpm * 6 * 17 * E
lpf
=
15.6 + 1.4 = 17µs(typ)
= ArcTan [rpm / (60 * f0)]
------------------------------------------------------------------------- -
2μs ∗ NewAngle OldAngle
Revision 1.8
1.406
-6
–
in degrees
Total Position Error (Δθ
0,0175º
0,175º
1,75º
pd +
Δ
θ
lpf
)
24 - 39
(EQ 1)
(EQ 2)
(EQ 3)
(EQ 4)