AMIS-30421 Datasheet, PDF (20/41 Pages) ON Semiconductor – Micro-Stepping Stepper Motor Bridge Controller

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Step 2
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AMIS−30421
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DIR−pin = low
Step 1
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Step 1
Step 2
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Step 3
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DIR pin = low
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1/4^th Stepping Mode
Half Step
Correct change to a lower stepping mode. Step 2 of 1/4^th
stepping mode is equal to Step 1 of half step stepping mode
(see Table 7). No offset or phase shift is created.
1/4^th Stepping Mode
Half Step
Incorrect change to a lower stepping mode. Step 1 of 1/4^th
stepping mode is not shared with a step in half step stepping
mode (see Table 7). An offset or phase shift will be created!
Figure 17. NXT−Step Mode Synchronization
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Step
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Step
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Step
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Step
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Half Step
Full Step
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Step
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Half Step
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Step
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Full Step
Half Step
Full Step
Figure 18. Changing to/from Full step Stepping Mode
Programmable Peak−Current
The amplitude of the current waveform in the motor coils
(I_max) can be programmed through SPI bits <CUR[2:0]>.
The coil current can be calculated as next:
I_max + <CUR[2:0}> ń R_SENSE
R_SENSE is resistor R₁ and R₂ as given in Figure 9.
A change in the coil current (<CUR[2:0]>) will be
updated at the next PWM cycle.
Clear
Logic 0 on the CLR−pin allows normal operation of the
chip. To clear the complete digital inside AMIS−30421, the
CLR−pin needs to be pulled to logic 1 for a minimum time
of t_CLR (Table 5). Clearing the motor driver can not be done
during Sleep Mode. During a clear the charge pump remains
active. The voltage regulator remains functional during and
after the clear action and the WDb−pin is not activated.
After a clear, NXT pulses can be applied after t_{CLR_SET}
(see Figure 7).
Speed and Load Angle Output
The SLA−pin provides an output voltage that indicates the
level of the BEMF (Back Electro Magnetic Force) voltage
of the motor. This BEMF voltage is sampled during every
so−called ”coil current zero crossing”. Per coil, two
zero−current positions exist per electrical period, yielding in
a total of four zero−current observation points per electrical
period.
Because of the relatively high recirculation currents in the
coil during current decay, the coil voltage V_COIL shows a
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