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Theory of Operation
Each circuit contains four main blocks (see Figure Chapter 2 .3):
1. Reference waveform generator
The microprocessor uses a D/A (digital to analog) converter to set
the desired level for the current in the stepper motor winding. The
output of the D/A converter varies in time to create a reference
waveform. This reference waveform is centered around 10V.
2. Motor current sense
The voltage across a series current sense resistor is measured
and level shifted so that it is centered around 5V.
3. Compare and control
This portion divides the output of the reference waveform
generator by two and compares it to the output of the motor
current sensor. Logic inside the gate array generates the control
signals for the power driver that applies voltage across the motor
winding in order to make the actual current match the reference
waveform.
4. Power driver
An H-bridge allows the supply voltage to be applied across the
winding in either polarity to drive the current to the desired value.
2-14
Figure Chapter 2 .3: Stepper Motor
CADJET 2
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