STSPIN820 Click Board™

Product Code: MIKROE-3544

The STSPIN820 Click Board™ is optimized for driving bipolar stepper motors over a wide voltage range. Therefore, the STSPIN820 integrates very efficient H-Bridges with ON resistance of approximately 1Ω through each bridge. Motor current can be limited by an onboard potentiometer. These features make the STSPIN820 Click Board™ perfectly suited for rapid development of various stepper motor applications, including ATM-related applications, toys, 3D printers, mechatronics, robotics-related applications, etc. How Does The STSPIN820 Click Board™ Work? The STSPIN820 Click Board™ is based on the STSPIN820, an advanced stepper motor driver produced by STMicroelectronics. The monolithic IC incorporates both the power MOSFETs and the logic circuitry necessary for simplified control and reliable functioning of the connected bipolar stepper motor. Featuring a microstepping sequencer that supports up to 256 microsteps, this IC can perform very smooth and silent movements. The step sequencer also controls the VREF voltage, allowing the current through coils to be at an optimal level during the microstepping.

In full step mode, the maximum current through the coils is controlled by the VREF, according to the formula given further below. As the sequencer propagates through the microsteps, the VREF is further reduced following a circular pattern, ensuring maximum power efficiency for each step. The STSPIN820 has two PWM current controllers with the fixed OFF time for each H-Bridge, during which the current decay sequence is performed. This effectively limits the maximum current through the connected motor phase. The OFF (decay) time is fixed to approximately 25 µs on this Click board™. The DECAY pin determines the decay mode. In mixed decay mode (DECAY pin at the LOW logic level), the decay period is divided into slow decaying and fast decaying segments. The slow decay segment lasts for 5/8 of the total OFF time, while the fast decay segment lasts for 3/8 of the total OFF time. When the DECAY pin is at the HIGH logic level, the slow decay mode lasts for the entire OFF time. The PWM current controller compares the voltage across two sense resistors (VSENS1, and VSENS2) and the VREF voltage, which can be adjusted by a potentiometer. When VSENS becomes greater than the VREF voltage, the current limiting is triggered, and the OFF timer starts counting. The decay sequence is performed. By using a simple formula, the VREF voltage can be determined for a specific load current: VREF = RSENS · ILOAD Where: VREF is the voltage on the REF pin of the STSPIN820, adjustable with the potentiometer. RSENS is the resistance of the current sensing resistor, which is 330 mΩ. ILOAD is the peak current through the motor coils. By knowing the RSENS, it can be easily calculated how much voltage should be applied to the REF pin of the STSPIN820, to limit the current according to ILOAD. For example, if there is 0.3V applied at the VREF pin, the current limit will be maxed out to 0.91A. The potentiometer allows to simply adjust the VREF voltage, according to needs. The STSPIN820 contains two independent H-Bridges, and each of them controls one phase of the bipolar stepper motor. The motor can be controlled by using these pins: DIR, STCK, RST, EN, and FAULT. The DIR pin determines the direction of the rotation. If set to a HIGH logic level, the internal microstepping counter will increase its value with each pulse coming through the STCK pin. The LOW logic level on this pin will cause the microstepping sequencer to decrease its counter. DIR pin is routed both to the mikroBUS™ pin AN (labelled as DIR). STCK pin has already been explained above: a pulse on this pin will cause the microstepping sequencer to increase or decrease its counter, depending on the state of the DIR pin. SW1, SW2, and SW3 switches on the Click board™ are used to determine the step size. They have MODE 1, MODE 2, and MODE 3 pins routed to them, respectively. All these switches can be used to set the mode at any moment during the operation. The changes are applied immediately. The datasheet of the STSPIN820 IC offers a truth-table which contains settings of these switches for each microstepping mode. The STBY/RESET (RST) pin of the STSPIN820 is used to set both bridge outputs in HIGH-Z mode, disconnecting the power supply from the H-Bridges. This pin allows lower average power consumption as no current can flow from the power supply to the motor. This pin is routed to the RST pin of the mikroBUS™. The control logic circuitry will be reset when leaving the standby mode. The EN/FAULT (EN) pin has a double purpose: when set to a high logic level, it acts as a chip enable, allowing the device to operate. In the case of a fault condition on the IC, it will be asserted to a LOW logic level, acting as an interrupt pin. After a timeout period defined by the external capacitor and resistor values, a restart attempt will be made. This pin is routed to both CS an