33970 datasheet(28/36 Pages) FREESCALE

28 / 36 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33970

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

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.

VELOCITY

n=0

HOLDCNT = 2

STEPS

33970 Datasheet(PDF) 28 Page - Freescale Semiconductor, Inc

33970 Datasheet(HTML) 28 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL