DM420Y digital stepper driver

Introduction

I had to order a small stepper motor for my pick-and-place machine. It had burnt out and needed replacement. The only place that has them is Stepper Online. During ordering, I saw they had ‘digital’ stepper motor drivers. The name caught my attention, the price for DM420Y – their smallest version – was just €15,- shipped from Germany.

The DM420Y is aimed at driving NEMA 14,17, and 23 type steppers and can handle up to 2.2A (1.6A RMS). They claim it uses 32-bit DSP control technology and that made me want to know what is inside.. so I bought one.

The stepper driver I got has more features than I expected. The image below is the one from Stepper Online:

The image shows far fewer settings for the microstepping configuration. The driver I have uses three switches, while the image shows only two are used. In addition, the opto-isolated step/dir/fault pins were upgraded from 5V only to a 5..24V range.

Internals

Of course, a few moments after it arrived the screws were taken out and the warranty voided.

Top side

Here is an image of the top side of the PCB:

The 38-pin TSSOP chip is an ARM Cortex M0 made by Infineon. The part number is XMC1302-T038X0032. It runs at up to 32 MHz but the peripherals can run up to 64 MHz. Infineon added a math co-processor which performs CORDIC operations and provides a divider in hardware. It was specially designed for motor control operations; the timers support dead-time generation and there are 8! of them. It also has special peripherals for incremental encoders and hall current sensors. This is also the only 5V ARM Cortex processor I’ve seen.

The rest of the ICs are very common. There is an LM324 quad opamp (just above the blue DIP sitches). An TL272C dual opamp (covered by the white goo). And an 74HC14 hex-inverter/schmitt trigger.

Also visible are four large 25mOhm current sense resistors.

Bottom side

Here is an image of the bottom side of the PCB:

The setup now becomes more clear. There are three opto-couplers (to the bottom left) that isolate the digital control pins from the rest of the circuit. On the top right there is a coil and a switch-mode power supply IC that generates 5V for the digital part. Below that are four Infineon/International Rectifier IRFS2103 gate driver ICs. They have internal dead-time generators and can drive both the high-side and low-side MOSFETs of an H-bridge. Speaking of which, below the gate drivers are four dual MOSFETs packaged in SOIC-8, part number IRF7351. They can handle up to 6A of continuous current and have an RDSon of 18mOhms.

The MOSFETs are not in thermal contact with the aluminium housing, which I found a bit disappointing. However, at the maximum setting of 2.2A the RDSon of the MOSFETs is so low that they’ll only dissipate 90mW each. I’m sure the switching losses will add to the heating but the MOSFETs might not need heatsinking after all.

Additional stuff

Both sides of the PCB are covered in some sort of protective coating. I was able to get some of it off the chips with some acetone and elbow grease to read the part numbers.

The black 4-pin connector is probably exposes a UART while the white 4-pin connector goes to the SWD debug/programming pins of the microcontroller. I haven’t checked if the SWD port is active as it uses 5V signalling and I don’t have a debug probe capable of that voltage.

Conclusion

The DM420Y is a well-built module with a discrete MOSFET H-bridge setup driven by a 32-bit ARM Cortex M0 microcontroller. Amazing what you get for the asking price.