CNC Dictionary. Ive produced this dictionary to make it easier to understand the definitions of the various arcane terms used in CNC. Disclaimer. This product is designed as an aid for customers of Texas Instruments. No warranties, either expressed or implied, with respect to this third party. Stepper motor performance is strongly dependent on the driver circuit. Torque curves may be extended to greater speeds if the stator poles can be reversed more. A4. 98. 8 Stepper Motor Driver Carrier. A4. 98. 3A4. 98. Overview. This product is a carrier board or breakout board for Allegros A4. DMOS Microstepping Driver with Translator and Overcurrent Protection we therefore recommend careful reading of the A4. We offer excellent stepper motor, Stepper Motor Driver, DC Servo Motor, Stepper Motor Power Supply, Stepper Motor Kit, CNC router. These are the best motors on the. MB pdf before using this product. This stepper motor driver lets you control one bipolar stepper motor at up to 2 A output current per coil see the Power Dissipation Considerations section below for more information. Here are some of the drivers key features Simple step and direction control interface. Five different step resolutions full step, half step, quarter step, eighth step, and sixteenth step. Adjustable current control lets you set the maximum current output with a potentiometer, which lets you use voltages above your stepper motors rated voltage to achieve higher step rates. Intelligent chopping control that automatically selects the correct current decay mode fast decay or slow decayOver temperature thermal shutdown, under voltage lockout, and crossover current protection. Short to ground and shorted load protection. This product ships with all surface mount componentsincluding the A4. ICinstalled as shown in the product picture. This product ships individually packaged with 0. For customers interested in higher volumes at lower unit costs, we offer a bulk packaged version without header pins and a bulk packaged version with header pins installed. Note that we carry several stepper motor drivers that can be used as alternatives for this module and drop in replacements in many applications The Black Edition A4. Black Edition and this green board are interchangeable. The DRV8. 82. 5 carrier offers approximately 5. The DRV8. 83. 4 carrier works with motor supply voltages as low as 2. V, making it suitable for low voltage applications. The DRV8. 88. 0 carrier offers dynamically scalable current limiting and Auto. Tune, which automatically selects the decay mode each PWM cycle for optimal current regulation performance based on factors like the motor winding resistance and inductance and the motors dynamic speed and load. We also sell a larger version of the A4. V and 3. 3 V voltage regulators that eliminate the need for separate logic and motor supplies. Some unipolar stepper motors e. Driving Unipolar Stepper With Bipolar Driver' title='Driving Unipolar Stepper With Bipolar Driver' />For more information, please see the frequently asked questions. Unipolar motors with five leads cannot be used with this driver. Included hardware. The A4. 98. 8 stepper motor driver carrier comes with one 11. The headers can be soldered in for use with solderless breadboards or 0. You can also solder your motor leads and other connections directly to the board. A version of this board with headers already installed is also available. Using the driver. Minimal wiring diagram for connecting a microcontroller to an A4. Power connections. The driver requires a logic supply voltage 3 5. V to be connected across the VDD and GND pins and a motor supply voltage 8 3. V to be connected across VMOT and GND. These supplies should have appropriate decoupling capacitors close to the board, and they should be capable of delivering the expected currents peaks up to 4 A for the motor supply. Warning This carrier board uses low ESR ceramic capacitors, which makes it susceptible to destructive LC voltage spikes, especially when using power leads longer than a few inches. Under the right conditions, these spikes can exceed the 3. V maximum voltage rating for the A4. V. One way to protect the driver from such spikes is to put a large at least 4. F electrolytic capacitor across motor power VMOT and ground somewhere close to the board. Motor connections. Four, six, and eight wire stepper motors can be driven by the A4. FAQ answer explains the proper wirings in detail. Warning Connecting or disconnecting a stepper motor while the driver is powered can destroy the driver. More generally, rewiring anything while it is powered is asking for trouble. Step and microstep size. Stepper motors typically have a step size specification e. A microstepping driver such as the A4. For instance, driving a motor in quarter step mode will give the 2. The resolution step size selector inputs MS1, MS2, and MS3 enable selection from the five step resolutions according to the table below. MS1 and MS3 have internal 1. MS2 has an internal 5. For the microstep modes to function correctly, the current limit must be set low enough see below so that current limiting gets engaged. Otherwise, the intermediate current levels will not be correctly maintained, and the motor will skip microsteps. MS1. MS2. MS3. Microstep Resolution. Low. Low. Low. Full step. High. Low. Low. Half step. Low. High. Low. Quarter step. High. High. Low. Eighth step. Alaska Ultimate X. High. High. High. Sixteenth step. Control inputs. Each pulse to the STEP input corresponds to one microstep of the stepper motor in the direction selected by the DIR pin. Note that the STEP and DIR pins are not pulled to any particular voltage internally, so you should not leave either of these pins floating in your application. If you just want rotation in a single direction, you can tie DIR directly to VCC or GND. The chip has three different inputs for controlling its many power states RST, SLP, and EN. For details about these power states, see the datasheet. Please note that the RST pin is floating if you are not using the pin, you can connect it to the adjacent SLP pin on the PCB to bring it high and enable the board. Current limiting. One way to maximize stepper motor performance is to use as high of a voltage as is practical for your application. In particular, increasing the voltage generally allows for higher step rates and stepping torque since the current can change more quickly in the coils after each step. However, in order to safely use voltages above the rated voltage of a stepper motor, the coil current must be actively limited to keep it from exceeding the motors rated current. The A4. 98. 8 supports such active current limiting, and the trimmer potentiometer on the board can be used to set the current limit. One way to set the current limit is to put the driver into full step mode and measure the current running through a single motor coil while adjusting the current limit potentiometer. This should be done with the motor holding a fixed position i. STEP input. Note that the current you are measuring is only 7. Also, note that you will need to perform this adjustment again if you ever change the logic voltage, Vdd, since the reference voltage that sets the current limit is a function of Vdd. Note The coil current can be very different from the power supply current, so you should not use the current measured at the power supply to set the current limit. The appropriate place to put your current meter is in series with one of your stepper motor coils. Another way to set the current limit is to calculate the reference voltage that corresponds to your desired current limit and then adjust the current limit potentiometer until you measure that voltage on the VREF pin. The VREF pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board. The current limit, IMAX, relates to the reference voltage as follows IMAX VREF 8 RCSor, rearranged to solve for VREF VREF 8 IMAX RCSRCS is the current sense resistance original versions of this board used 0. January 2. 01. 7, which makes more of the adjustment potentiometers range useful. The following picture shows how to identify which current sense resistors your board has Identification of original 5. January 2. 01. 7. So, for example, if you want to set the current limit to 1 A and you have a board with 6. VREF to 5. 40 m. V.