33970 Datasheet, PDF (29/36 Pages) Freescale Semiconductor, Inc – Dual Gauge Driver Integrated Circuit with Improved Damping Algorithms

FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
I_MAX
I_COIL
0
I_MAX
0
1
I_MAX
I_COIL
0
SINE
2
COSINE
3
0
I_MAX
0
1
2
3
0
Figure 12. Full Steps Counterclockwise
The IC automatically prepares the non-driven coil at each
step, waits for a predetermined blanking time, then
processes the signal for the duration of the full step. When
the pointer reaches the stop and no longer moves, the
dissipating flux is detected. The processed results are placed
in the RTZ accumulator, then compared to a decision
threshold. If the signal exceeds the decision threshold, the
pointer is assumed to be moving. If the threshold value is not
exceeded, the drive sequence is stopped if RTZR bit RZ4 is
logic [0]. If bit RZ4 is logic [1], the RTZ movement will
continue indefinitely until the RTZR bit RZ1 is used to stop the
RTZ event.
A pointer that is not on a full step location or that is in
magnetic alignment prior to the RTZ event may cause a false
RTZ detection. More specifically, an RTZ event beginning
from a non-full step position may result in an abbreviated
integration value potentially interpreted as a stalled pointer.
Advancing the pointer by at least 12 microsteps clockwise (if
PE7 = 0) to the nearest full step position (e.g., 0, 6, 12, 18,
24, etc.) prior to initiating an RTZ ensures the magnetic fields
line up and increases the chances of a successful pointer
stall detection. It is important that the pointer be in a static, or
commanded, position before starting the RTZ event.
Because the time duration and the number of steps the
pointer moves prior to reaching the commanded position can
vary depending upon its status at the time a position change
is communicated, the master should assure sufficient
elapsed time prior to starting an RTZ. If an RTZ is desired
after first enabling the outputs or after forcing a reset of the
device, the pointer should first be commanded to move 12
microsteps clockwise to the nearest full step location.
Because the pointer was in a static position at default, the
master could determine the number of microsteps the device
has taken by monitoring and counting the MOV0. MOV1
device status bit transitions to confirm the pointer is again in
a static position. Alternatively, the user could monitor the
device status bits CMD1 and CMD2.
Only one gauge at a time can be returned to the zero
position. The gauge not returning to zero can continue to be
controlled. An RTZ should not begin until the gauge to be
calibrated is at a static position and its pointer is at a full step
position. An attempt to calibrate a gauge while the other is in
the process of an RTZ event is ignored by the device. In most
applications of the RTZR command, it is possible to avoid a
visually obvious sequential calibration by first bringing the
pointers back close to their previous zero positions, then re-
calibrating them sequentially.
After completion of an RTZ, the 33970 automatically
assigns the zero-step position to the full step position at the
end-stop location. Because the actual zero position could lie
anywhere within the full step where the zero was detected,
the assigned zero position could be within a window of ±0.5
degree. An RTZ can be used to detect stall, even if the
pointer already rests on the end stop when an RTZ sequence
is initiated. However, it is recommended the pointer be
advanced by at least 12 microsteps to the nearest full step
prior to initiating the RTZ.
RTZ OUTPUT
During an RTZ event the non-driven coil is analyzed to
determine the state of the motor. The 33970 multiplexes the
coil voltages and provides the signal from the non-driven coil
to the RTZ pin.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33970
29