33970 datasheet(29/36 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33970

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

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.

COSINE

SINE

IMAX

ICOIL

IMAX

33970 Datasheet(PDF) 29 Page - Freescale Semiconductor, Inc

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