33970 Datasheet, PDF (28/36 Pages) Freescale Semiconductor, Inc – Dual Gauge Driver Integrated Circuit with Improved Damping Algorithms

FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
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VELOCITY
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Acceler1^at11^e21314151617
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Decelerate
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HOLDCNT = 2
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STEPS
Figure 11. Deceleration Ramp
RETURN TO ZERO CALIBRATION
Many step motor applications require that the IC detect
when the motor is stalled after commanded to return to the
zero position for calibration purposes. The stalling occurs
when the pointer hits the end stop on the gauge bezel, which
is usually at the zero position. It is important that when the
pointer reaches the end stop it immediately stops without
bouncing away.
The 33970 device provides the ability to automatically and
independently return each of the two pointers to the zero
position via the RTZR and RTZCR SPI commands. An
automatic RTZ is initiated using the RZ0, RZ1, and RZ2 bits.
Unconditional RTZ movement is initiated using the RZ0, RZ2,
and RZ4 bits. During an RTZ event, all commands related to
the gauge being returned are ignored until the pointer has
successfully zeroed or the RTZR bit RZ1 is written to disable
the event. Once an RTZ event is initiated, the device reports
back via the SO pin that an RTZ is underway.
The RTZCR command is used to set the RTZ pointer
speed, choose an appropriate blanking time, and preload the
integration accumulator with an appropriate offset. On
reaching the end stop, the device reports back to the
microcontroller via the status message that the RTZ was
successful. The RTZ automatically disables, allowing other
commands to be valid. In the event the master determines an
RTZ sequence is not working properly (i.e., the RTZ taking
too long), it can disable the command via the RTZR bit RZ1.
RTZCR bits RC10:RC5 are written to preload the
accumulator with a predetermined value that will assure an
accurate pointer stall detection. This preloaded value is
determined during application development by disabling the
automatic shutdown feature of the device with the RTZR bits
RZ4 and RZ2. This operating mode allows the master to
monitor the RTZ event, using the accumulator information
available via the SO if the device is configured to provide the
RTZ Accumulator Status. The unconditional RTZ event can
be turned OFF using the RTZR bit RZ1.
If the Position 0 location bit is in the default logic [0] mode,
then during an RTZ event the pointer is returned counter-
clockwise (CCW) using full steps at a constant speed
determined by the RTZCR RC3:RC0 and RC12:RC11 bits
during RTZ configuration (see Figure 12). Full steps are used
during an RTZ so that only one coil of the motor is being
driven at any time. The coil not being driven is used to
determine if the pointer is moving. If the pointer is moving, the
EMF signal that is present in the non-driven coil is processed
by integrating the signal present on the opened pin of the coil
while essentially grounding the other end.
33970
28
Analog Integrated Circuit Device Data
Freescale Semiconductor