AS5035_08 Datasheet, PDF (11/18 Pages) ams AG – PROGRAMMABLE 64 PPR INCREMENTAL MAGNETIC ROTARY ENCODER

AS5035 – 64 PPR INCREMENTAL MAGNETIC ROTARY ENCODER
10.4 Output Delays
10.5.3 Timing Tolerance over Temperature
Due to the sampling rate of 10kHz, there will be a delay
of up to 100µs between the time that the sample is taken
until it is converted and available as angular data.
A rotating magnet will therefore cause an angular error
caused by the output delay.
The internal RC oscillator is factory trimmed to ±5%.
Over temperature, this tolerance may increase to ±10%.
Generally, the timing tolerance has no influence in the
accuracy or resolution of the system, as it is used mainly
for internal clock generation.
This error increases linearly with speed:
e_sampling = rpm ∗ 6E ^−4
11 Failure Diagnostics
At low speeds this error is small (e.g. <= 0.06° at 100
lid ^rpm).
At speeds over 586 rpm, the error approaches 1LSB
(0.35°). The maximum error caused by the sampling rate
a _{of the ADCs is 0/+100µs. It has a peak of 1LSB = 0.35°}
at 586 rpm.
v _{At higher speeds this error is reduced again due to}
ill ^{interpolation and the output delay remains at 200µs}
as the DSP requires two sampling periods (2x100µs) to
synthesize and redistribute any missing pulses.
AG ^{t st 10.5 Temperature}
10.5.1 Magnetic Temperature Coefficient
s ⁿ _{One of the major benefits of the AS5035 compared to}
e _{linear Hall sensors is that it is much less sensitive to}
m ^{t temperature. While linear Hall sensors require a}
compensation of the magnet’s temperature coefficients,
a ^{n the AS5035 automatically compensates for the varying}
magnetic field strength over temperature. The magnet’s
o _{temperature drift does not need to be considered, as the}
c ^{AS5035 operates with magnetic field strengths from}
±45…±75mT.
al _Example:
A NdFeB magnet has a field strength of
ic ^{75mT @ –40°C and a temperature coefficient of}
-0.12% per Kelvin. The temperature change is from
n ^{–40° to +125° = 165K.}
The magnetic field change is: 165 x -0.12% = -19.8%,
h which corresponds to
75mT at –40°C and 60mT at 125°C .
c _{The AS5035 can compensate for this temperature related}
e field strength change automatically, no user adjustment
T^{is required.}
The AS5035 also offers several diagnostic and failure
detection features:
11.1 Magnetic Field Strength Diagnosis
Pins #1 (MagINCn) and #2 (MagDECn) are open-drain
outputs and will both be turned on (= low with external
pull-up resistor) when the magnetic field is out of range.
If only one of the outputs is low, the magnet is either
moving towards the chip (MagINCn) or away from the
chip (MagDECn).
11.2 Power Supply Failure Detection
11.2.1 MagINCn and MagDECn Pins:
These are open drain outputs and require external pull-
up resistors. In normal operation, these pins are high
ohmic and the outputs are high (see Table 2). In a failure
case, either when the magnetic field is out of range or
the power supply is missing, these outputs will become
low. To ensure adequate low levels in case of a broken
power supply to the AS5035, the pull-up resistors
(>10kΩ) must be connected to the positive supply at pin
16 (VDD5V).
11.2.2 Incremental Outputs:
In normal operation, pins A(#3), B(#4) and Index (#6) will
never be high at the same time, as Index is only high
when A=B=low. However, after a power-on-reset, if VDD
is powered up or restarts after a power supply
interruption, all three outputs will remain in high state
until pin CSn is pulled low (see 5.4.2 ). If CSn is already
tied to VSS during power-up, the incremental outputs will
all be high until the internal offset compensation is
finished (within tPwrUp).
Another way to detect a power supply loss is by
connecting pull-up resistors to the A,B and Index pins at
the receiving side (µC, control unit, etc..). If the negative
power line to the sensor is interrupted, all three outputs
will be pulled high by the external pull-up resistors. This
10.5.2 Accuracy over Temperature
The influence of temperature in the absolute accuracy is
unique state again indicates a failure as it does not occur
in normal operation.
very low. While the accuracy is ≤ ±0.5° at room
temperature, it may increase to ≤±0.9° due to increasing
noise at high temperatures.
Revision 1.5
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