# AMIS-30543 Stepper Motor Driver Carrier

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This is a breakout board for ON Semiconductor’s AMIS-30543 microstepping bipolar stepper motor driver, which features SPI-adjustable current limiting, 11 step modes (from full-step through 1/128-step), back-EMF feedback that can be used for stall detection or optional closed-loop control, and over-current and over-temperature protection. The board operates from 6 V to 30 V and can deliver up to approximately 1.8 A per phase without a heat sink or forced air flow (it is rated for 3 A per coil with sufficient additional cooling).

I want to control a 3.6 V, 2 A per phase bipolar stepper motor like this, but your AMIS-30543 stepper motor driver carrier has a minimum operating voltage of 6 V. Can I use this driver without damaging the stepper motor?

Yes. To avoid damaging your stepper motor, you want to avoid exceeding the rated current, which is 2 A in this instance. The AMIS-30543 stepper motor driver lets you limit the maximum current, so as long as you set the limit below the rated current, you will be within spec for your motor, even if the voltage exceeds the rated voltage. The voltage rating is just the voltage at which each coil draws the rated current, so the coils of your stepper motor will draw 2 A at 3.6 V. By using a higher voltage along with active current limiting, the current is able to ramp up faster, which lets you achieve higher step rates than you could using the rated voltage.

If you do want to use a lower motor supply voltage (under 6 V) for other reasons, consider using our DRV8834 low-voltage stepper motor driver carrier.

Do I really need to set the current limit on my stepper motor driver before using it, and if so, how do I do it?

Yes, you do! Setting the current limit on your stepper motor driver carrier is essential to making sure that it runs properly. An appropriate current limit also ensures that your motor is not allowed to draw more current than it or your driver can handle, since that is likely to damage one or both of them.

Setting the current limit on our AMIS-30543 stepper motor driver carrier is done through its SPI interface (this is very different from our A4988, DRV8825, DRV8824, DRV8834, DRV8880, and TB67S249FTG stepper motor driver carriers, which have their current limits set through their on-board potentiometers). The AMIS-30543 defaults to its lowest possible current limit (132 mA) when it is first enabled; you will need to set this to an appropriate value for your stepper motor before your system will work properly. The AMIS-30543 data sheet (495k pdf) has more information on how to set the current limit through the SPI interface, and our AMIS-30543 Arduino library includes an example sketch showing how to implement this in software.

My AMIS-30543 stepper motor driver is overheating, but my power supply shows it’s drawing significantly less than 1.8 A per coil. What gives?

Measuring the current draw at the power supply does not necessarily provide an accurate measure of the coil current. Since the input voltage to the driver can be significantly higher than the coil voltage, the measured current on the power supply can be quite a bit lower than the coil current (the driver and coil basically act like a switching step-down power supply). Also, if the supply voltage is very high compared to what the motor needs to achieve the set current, the duty cycle will be very low, which also leads to significant differences between average and RMS currents: RMS current is what is relevant for power dissipation in the chip but many power supplies won’t show that. You should base your assessment of the coil current on what the limit has been set to (through the SPI interface) or by measuring the actual coil currents.

While the AMIS-30543 driver IC is rated for up to 3 A (peak) per coil, the chip by itself will overheat at lower currents. We have found that it generally requires a heat sink to deliver more than approximately 1.8 A per coil, but this number depends on factors such as ambient temperature and air flow. For example, sealing three driver carriers in close proximity in a small box will cause them to overheat at lower currents than a unit by itself in open air. It is worth noting that it is possible to use the SPI-configurable current limit to selectively deliver higher currents for short durations without overheating the driver.

How do I connect my stepper motor to the AMIS-30543 stepper motor driver carrier?

The answer to this question depends on the type of stepper motor you have. When working with stepper motors, you will typically encounter two types: unipolar stepper motors and bipolar stepper motors. Unipolar motors have two windings per phase, allowing the magnetic field to be reversed without having to reverse the direction of current in a coil, which makes unipolar motors easier to control than bipolar stepper motors. The drawback is that only half of the phase is carrying current at any given time, which decreases the torque you can get out of the stepper motor. However, if you have the appropriate control circuitry, you can increase the stepper motor torque by using the unipolar stepper motor as a bipolar stepper motor (note: this is only possible with 6- or 8-lead unipolar stepper motors, not with 5-lead unipolar stepper motors). Unipolar stepper motors typically have five, six, or eight leads.

Bipolar steppers have a single coil per phase and require more complicated control circuitry (typically an H-bridge for each phase). The AMIS-30543 has the circuitry necessary to control a bipolar stepper motor. Bipolar stepper motors typically have four leads, two for each coil.

The above diagram shows a standard bipolar stepper motor. To control this with the AMIS-30543, connect stepper leads A and C to board outputs MOTXP and MOTXN, respectively, and stepper leads B and D to board outputs MOTYP and MOTYN, respectively. Note that if you happen to swap which way the wires are connected for any coil, the stepper motor will turn in the opposite direction, and if you happen to pair up wires from different coils, the motor should be noticeably erratic when you try to step it, if it even moves at all. See the AMIS-30543 datasheet for more information.

If you have a six-lead unipolar stepper motor as shown in the diagram below:

you can connect it to the AMIS-30543 as a bipolar stepper motor by making the bipolar connections described in the section above and leaving stepper leads A’ and B’ disconnected. These leads are center taps to the two coils and are not used for bipolar operation.

If you have an eight-lead unipolar stepper motor as shown in the diagram below:

you have several connection options. An eight-lead unipolar stepper motor has two coils per phase, and it gives you access to all of the coil leads (in a six-lead unipolar motor, lead A’ is internally connected to C’ and lead B’ is internally connected to D’). When operating this as a bipolar stepper, you have the option of using the two coils for each phase in parallel or in series. When using them in parallel, you decrease coil inductance, which can lead to increased performance if you have the ability to deliver more current. However, since the AMIS-30543 actively limits the output current per phase, you will only get half the phase current flowing through each of the two parallel coils. When using them in series, it’s like having a single coil per phase (like in four-lead bipolar steppers or six-lead unipolar steppers used as bipolar steppers). We recommend you use a series connection.

To connect the phase coils in parallel, connect stepper leads A and C’ to board output MOTXP, stepper leads A’ and C to board output MOTXN, stepper leads B and D’ to board output MOTYP, and stepper leads B’ and D to board output MOTYN.

To connect the phase coils in series, connect stepper lead A’ to C’ and stepper lead B’ to D’. Stepper leads A, C, B, and D should be connected to the stepper motor driver as normal for a bipolar stepper motor (see the bipolar stepper connections above).

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