PC33991DHSLASHR2 datasheet(26/36 Pages) MOTOROLA

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33991

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

calibration procedure was not successful. A clock calibration is

allowed only if the gauges are disabled or the pointers are not

moving, indicated by status bits ST4 and ST5.

Figure 7. Gauge Enable and Clock Calibration Example

Some applications may require a guaranteed maximum

pointer velocity and acceleration. Guaranteeing these

maximums requires the nominal internal clock frequency fall

below 1 MHz. The frequency range of the calibrated clock is

always below 1 MHz if PECR bit D4 is logic [0] when initiating a

calibration command, followed by an 8 µs reference pulse. The

frequency is centered at 1 MHz if bit D4 is logic [1].

The 33991 can be deceived into calibrating faster or slower

than the optimal frequency by sending a calibration pulse longer

or shorter than the intended 8 µs. As long as the count remains

between four and 15 there is no clock calibration flag. For

applications requiring a slower calibrated clock, i.e., a motor

designed with a gear ratio of 120:1 (8 microsteps/degrees), a

longer calibration pulse is required. The device allows a SPI

selectable slowing of the internal oscillator, using the PECR

command so the calibration divisor safely falls within the four to

15 range when calibrating with a longer time reference. For

example, for the 120:1 motor the pulse would be 12 µs instead

of 8 µs. The result of this slower calibration results in the longer

step times necessary to generate pointer movements

meetingthe acceleration and velocity requirements. The

resolution of the pointer positioning decreases from 0.083

°/

microstep (180:1) to 0.125

°/microstep (120:1). The pointer

sweep range increases from approximately 340

° to over 500°.

Note:

Be aware a fast calibration could result in violations of the

motor acceleration and velocity maximums, resulting in missed

steps.

Pointer Deceleration Waveshaping

Constant acceleration and deceleration of the pointer results

in choppy movements when compared to air core movements.

Air core behavior can be simulated with appropriate wave

shaping during deceleration only. This shaping is achieved by

adding repetitive steps at several of the last step values. An

example is illustrated in Figure 8.

Figure 8. Deceleration Waveshaping

SCLK

CSB

PECR Command

8us Calibration Pulse

D15

Figure 5-2 Gauge Enable & Clock Calibration Example

SCLK

HOLDCNT=

n =

VELOCITY

lera

STEPS

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

PC33991DH/R2 Datasheet(PDF) 26 Page - Motorola, Inc

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