AMIS-30421 Datasheet, PDF(14/41 Page) ON Semiconductor – Micro-Stepping Stepper Motor Bridge Controller

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AMIS-30421 Datasheet, PDF (14/41 Pages) ON Semiconductor – Micro-Stepping Stepper Motor Bridge Controller

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AMISâ30421

PWM Current Control

A PWM comparator compares continuously the actual

winding current (measured over the external sense resistor)

with the requested current and feeds back the information to

a digital regulation loop. This loop then generates a PWM

signal, which turns on/off the current sources (Ion, Ioff) and

switches (SWon, SWoff). The switching points of the PWM

dutyâcycle are synchronized to the onâchip PWM clock.

The frequency of the PWM controller is fixed and will not

vary with changes in the supply voltage. Also variations in

motorâspeed or loadâconditions of the motor have no effect.

There are no external components required to adjust the

PWM frequency.

For EMC reasons itâs possible to add jitter to the PWM by

means of the <PWMJ> bit.

Step Translator and Step Mode

The step translator provides the control of the motor by

means of the stepmode SPI bits <SM[2:0]>, the enable SPI

bit <MOTEN>, the direction SPI bit <DIRCTRL> and input

DIRâpin = high

Step 7

Start = 0

DIRâpin = low

Step 1

Step 6

Step 5

Step 2

Step 4

Step 3

pins DIR and NXT. It is translating consecutive steps in

corresponding currents in both motor coils for a given step

mode. One out of 8 possible stepping modes can be selected

through SPI bits <SM[2:0]>.

After powerâup or clear (CLRâpin) the coil current

translator is set to position 0. For all stepping modes except

full step this means that the coil current is maximum in the

Yâcoil and zero in the Xâcoil (see Table 7). If NXT pulses

are applied when the DIRâpin is pulled low, SPI bit

<DIRCTRL> is zero and SPI bit <MOTEN> is one, the coil

current translator will step through Table 7 from top till

bottom. If DIRâpin is pulled high or SPI bit <DIRCTRL> is

set to â1â, the coil current translator will step in opposite

direction through the table.

Figures 12 up to 15 gives another view on the different

stepping modes. The Yâcoil current is plotted on the

Yâaxes, the Xâcoil current on the Xâaxes. Notice that all

stepping modes from Table 7 can be plotted on a circle with

the exception of half step uncompensated and full step.

These are plotted on a square.

DIRâpin = high

Start = 0

Step 15

Step 14

Step 13

Step 1

DIRâpin = low

Step 2

Step 3

Step 12

Step 11

Step 10

Step 9

Step 4

Step 5

Step 6

Step 7

Step 8

Figure 12. Circular representation Halfâstep

Compensated

DIRâpin = high

Step7

Start= 0

DIRâpin = low

Step 1

Figure 13. Circular representation 1/4

Microstepping

DIRâpin = high

Start= 0

DIRâpin = low

Step 1

Step2

Step 6

Step5

Step4

Step 3

Step3

Step2

Figure 14. Square Representation Halfâstep

Uncompensated

Figure 15. Square Representation

Fullâstep

Remark:

â¦ Positive coil current flows from MOTXP to MOTXN and MOTYP to MOTYN.

â¦ In above figures SPI bit <DIRCTRL> is set to â0â. When set to â1â, rotation will be reversed.

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