33991
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Figure 9. Full Steps (CCW)
RTZ Output
The non-driven coil is analyzed determining the state of the
motor during an RTZ event. The 33991multiplexes the coil
voltages and provides the signal from the non-driven coil to the
RTZ pin.
Default Mode
Default mode refers to the state of the 33991after an internal
or external reset and prior to SPI communication. An internal
reset occurs during V
DD
power-up. An external reset is initiated
by the RST pin driven to a logic [0]. With the exception of the
RTZ
CR
full step time,allof the specific pin functionsandinternal
registers will operate as though all of the addressable
configuration register bits were set to logic [0]. This means for
example, all of the outputs will be disabled after a power-up or
external reset, SO flag ST6 is set, indicating an under voltage
event. Anytime an external reset is exerted and the default is
restored, all configuration parameters, e.g., clock calibration,
maximum speed, RTZ parameters, etc. are lost and must be
reloaded.
Fault Logic Requirements
The 33991device indicates each of the following faults as
they occur:
Over temperature fault
Out-of-range voltage faults
Clock out of spec
Over current faults are notreporteddirectly. Itislikely,however,
an over current condition will become a thermal issue and be
reported.
Over Temperature Fault Requirements
The 33991incorporates over temperature protection
circuitry, shutting off the affected Gauge Driver when excessive
temperatures are measured. In the event of a thermal overload,
the affected gauge driver is automatically disabled. The over
temperature fault is flagged via ST0 and/or ST1. Its respective
flag continues to be set until the affected gauge is successfully
re-enabled, provided the junction temperature has fallen below
the hysteresis level.
Over Voltage Fault Requirements
The device is capable of surviving V
PWR
voltages within the
maximum specified in the
Maximum Ratings
table. V
PWR
levels
resulting in an Over Voltage Shut Down condition can result in
uncertain pointer positions. Therefore, the pointer position
should be re-calibrated. The master is then notified of an over
voltage event via the ST6 flag on the SO pin. Over voltage
detection and notification occurs regardless of whether the
gauge(s) are enabled or disabled.
Note:
There is no way to distinguish between an over voltage fault
and an under voltage fault from the status bits. If there is no external
means for the microcontroller to determine the fault type, the gauges
should be routinely enabled following the transition to logic [0] of ST6.
+
_
_
+
0
1
2
3
0
2
0
0
3
1
I
max
I
max
I
max
I
max
0
0
I
coil
I
coil
SINE
COSINE
F
Freescale Semiconductor, Inc.
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