AMIS-30624 Datasheet, PDF (16/56 Pages) AMI SEMICONDUCTOR – I2C Microstepping Motordriver

AMIS-30624 I²C Microstepping Motordriver
Data Sheet
14.0 Structural Description
See also the Block Diagram in Figure 1.
14.1 Stepper Motordriver
The motordriver receives the control signals from the control logic. The main features are:
• Two H-bridges designed to drive a stepper motor with two separated coils. Each coil (X and Y) is driven by one H-bridge and
the driver controls the currents flowing through the coils. The rotational position of the rotor, in unloaded condition, is defined
by the ratio of current flowing in X and Y. The torque of the stepper motor when unloaded is controlled by the magnitude of the
currents in X and Y.
• The control block for the H-bridges including the PWM control, the synchronous rectification and the internal current sensing
circuitry
• The charge pump to allow driving of the H-bridges’ high side transistors
• Two pre-scale 4-bit DACs to set the maximum magnitude of the current through X and Y
• Two DACs to set the correct current ratio through X and Y
Battery voltage monitoring is also performed by this block, which provides information to the control logic part. The same applies for the
detection and reporting of an electrical problem that could occur on the coils or the charge pump.
14.2 Control Logic (Position Controller and Main Control)
The control logic block stores the information provided by the I²C interface (in a RAM or an OTP memory) and digitally controls the
positioning of the stepper motor in terms of speed and acceleration, by feeding the right signals to the motordriver state machine.
It will take into account the successive positioning commands to properly initiate or stop the stepper motor in order to reach the set
point in a minimum time.
It also receives feedback from the motordriver part in order to manage possible problems and decide on internal actions and reporting
to the I²C interface.
14.3 Motion Detection
Motion detection is based on the back emf, generated internally in the running motor. When the motor is blocked, for example when it
hits the end-position, the velocity and as a result also the generated back emf, is disturbed. The AMIS-30624 senses the back emf,
calculates a moving average and compares the value with two independent threshold levels. If the back emf disturbance is bigger than
the set threshold, the running motor is stopped.
14.4 Miscellaneous
The AMIS-30624 also contains the following:
• An internal oscillator needed for the control logic and the PWM control of the motor driver
• An internal trimmed voltage source for precise referencing
• A protection block featuring a thermal shutdown and a power-on-reset circuit
• A 5V regulator (from the battery supply) to supply the internal logic circuitry
AMI Semiconductor – Apr. 2007, Rev 3.1, M-20664-003
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