A New Motor Driver for Three-Phase Battery-Operated Motors from STMicroelectronics

STMicroelectronics announces a new low-voltage three-phase and “three-sense” motor driver IC.

STMicroelectronics claims that the STSPIN233 from STMicro is well-suited for applications including toys, drones, and low-voltage electronic valves.

This new IC is actually very similar to another motor driver from STMicroelectronics, called the STSPIN230. The only major difference between these two ICs is that the STSPIN233 uses three shunt sensing technology, as opposed to the single shunt sensing method that is utilized in the STSPIN230 IC.

The figure below shows the block diagrams of these two devices along with their respective three-shunt and single-shunt current sensing methods (in the red boxes).

 

The STSPIN230's single-shunt technology (top figure) vs. the STSPIN233's triple-shunt technology (bottom figure). Images from the STSPIN230 and STSPIN233 datasheets (PDFs).

After reading through the STSPIN233 datasheet, as well as its product page, I wasn’t clear on the advantages that this three-shunt technology offers. But after doing a little digging (AKA Googling), I found a document produced by TI that states, on page 4, that "three-shunt measurement circuit[s]" have an advantage over single-shunt circuits in that they "can detect circulating currents." So, based on this information it appears that the STSPIN233's three-shunt sensing technology could allow for control of sensorless BLDC motors, rather than just traditional BLDC motors (i.e., those that have built-in sensors). But this is simply my best guess.

Do you have experience using triple-current-sensing motor drivers with sensorless BLDC motors? If so, please share your experiences in the comments section below.

Features and Protections

The STSPIN233 incorporates overcurrent, short-circuit, and thermal shutdown protection. Just for the record, though, these safeguards are common nowadays, and it would actually be out of the ordinary for a motor driver IC such as this one to not offer these features.

 

Thermal Protection

Regarding the thermal protection feature, it's a bit odd that the thermal protection threshold of 160°C is in fact 10°C higher than the listed absolute maximum T_J (junction temperature) value—see the figure below. What this implies is that once the thermal protection mechanism is engaged, the IC has been compromised, because the maximum junction temperature has been violated. Now, this is probably (hopefully) just a documentation oversight that ST didn't catch. But just to be sure, if you plan to use this part it would behoove you to reach out to ST asking for clarification regarding this protection value.

 

The IC's thermal shutdown threshold should be lower than the maximum junction temperature. Table taken from the datasheet (PDF).

 

Overcurrent Protection

On page 13 of the datasheet, within the section entitled Overcurrent and short-circuit protections, ST explains how the overcurrent disable time can be adjusted. ST offers a diagram and two equations (see the figure below) to illustrate how this feature works. I must say that the description associated with Equation 1 could use a little (or a lot of) attention from an editor.

 

The overcurrent disable time is user-adjustable. From the datasheet (PDF).

Typical Applications

Within Section 5 (entitled Typical applications) ST has provided a typical application circuit along with suggested external-component values (see the figure below). It should be noted, however, that the capacitors' voltage rating might require an increase depending on the voltage applied to the V_S pin. As a good rule of thumb, it's best to choose a capacitor with a voltage rating that's at least twice the voltage that you expect to apply across the capacitor. This IC has an operating voltage range of 1.8 to 10 V, and if it’s powered using a 10 V supply, the voltage rating of C_S and C_SPOL should be increased from 16 V to at least 20 V.

 

An application circuit with recommended component values; keep an eye on the capacitors’ voltage rating. Diagram and table taken from the datasheet (PDF).

 

While we’re on the topic of supply voltage, note that the voltage across the driver FETs will influence their on-state resistance. As you can see in the following plot, lower supply voltages lead to higher on-state resistance and, consequently, lower efficiency.

 

Power stage resistance vs. supply voltage. Plot taken from the the datasheet (PDF).

 

This is something to keep in mind if you have the option of using a higher motor-drive voltage.

 

Have you had a chance to use this new low-voltage, three-phase, three-sense motor driver IC in any of your designs? If so, leave a comment and tell us about your experiences.