Is The Servo Drive Unstable? Try A Dedicated Driver Chip To Save Space And Eliminate Interference With One Chip.

Have you ever encountered this situation when doing product innovation: you want to do theservocontrol yourself, but the discrete component solution takes up too much space and is troublesome to debug. The PCB is changed one version after another, but it is unstable? In fact, many engineers are stuck at this step, and I also came here from that time. The core of the problem is often not that the algorithm is bad, but that there is a lack of a chip specifically designed to do this job.

What exactly is a steering gear driver chip?

To put it bluntly,theservo-specific driver chipis just a circuit that used to be put together with a bunch of op amps, MOS tubes, and logic gates, all into a small black film. You only need to give it power, ground and PWM signals, and it can handle current detection, PID operation and H-bridge switching by itself. This thing is not some black technology, it is a chip specially optimized for positionservoapplications such as servos.

For example, TI's DRV83 series, and some domestic models have already solidified the underlying logic of dead time, overcurrent protection, and thermal shutdown. When you use it, you don’t have to worry about the size of the gate resistor or the type of freewheeling diode. The chip is all included.

Why does your servo always disobey?

Many makers use direct-drive servos, which are fine with small torque, but start to vibrate as soon as high current is applied. Or you can build an H-bridge yourself, but the result will be serious heating, and the tube will explode if the PWM frequency is slightly higher. The root cause is that the IO ports of ordinary MCUs are not suitable for directly driving power tubes. Level matching and driving capabilities are all pitfalls.

The core value of dedicated chips is to help you fill in the pits. Its built-in charge pump can boost and drive N-MOS, with an on-resistance of tens of milliohms and extremely low heat generation. The response speed of the current loop is microseconds, which is two orders of magnitude faster than writing interrupts yourself. To put it bluntly, it’s not that your code is bad, it’s that the tools are wrong.

How much trouble can be saved by using integrated chips?

️ The layout area is reduced by at least 60%

In the past, when making a dual-axis servo driver, the PCB was as big as a thumb no matter how compressed it was. Instead of adding two capacitors, the nail cap of the little finger can be put down. Use the saved space to install an encoder or wireless module, and the product will immediately have one more selling point.

️ Cut development cycle by more than half

There is no need to adjust the op amp bias, and there is no need to calculate the power consumption of the sampling resistor. The chip data manual will tell you directly: "To set the 5A current, write 0x32 in this register." Just fill in the parameters accordingly, and the probability of lighting up at one time is extremely high. Our team has a project that only took two weeks from drawing board to prototype, which was unimaginable before.

How to choose the right chip for your product

First check whether the voltage and current match. For toy servos below 6V, this low-voltage chip is enough; for robot joints between 12V and 24V, you must use this type of model with pre-drive. Don't use a small horse to pull a large cart, it will burn.

Then look at whether the packaging is suitable for your process. Use SOP for manual welding, QFN for machine placement, and WCSP if space is limited. Also, don’t forget to look at the sleep current. Battery-powered products must have standby microamps, otherwise users will scold them if they charge it every day.

Will the cost be skyrocketing?

You may think that dedicated chips are more expensive than transistors. Let’s do the math: a batch price is more than 2 yuan, and the discrete solution costs only 1.5 yuan for two half-bridge MOS. With the addition of op amps, sampling resistors, and protection diodes, the cost has long been exceeded. Not counting patch fees, debugging labor costs, and rework losses.

More importantly, using integrated chips allows you to change the PCB from a double-layer board to a single-layer board, and the cost of the board is directly discounted by 30%. Taken together, the cost of a single machine is actually reduced. After the quantity is large, you can negotiate the package price with the agent, and buy the MCU and driver chip together to get a more substantial discount.

Can domestic chips be printed now?

In the past, people did not trust domestic servo drive ICs because they thought they would be damaged by static electricity. Things have been completely different in the past two years. For products like Fengya and Lingdong Microelectronics, the ESD HBM can reach 8kV, and the overcurrent withstand time is 20% longer than similar products of a certain Texas Instruments. We have tested continuous forward and reverse rotation stalls. The domestic chip took 15 seconds to thermally protect, while the international brand stopped working in 10 seconds.

Moreover, the technical support from domestic manufacturers responds very quickly. Ask questions in the WeChat group at ten o'clock in the evening, FAE will reply within half an hour, and even directly send you a piece of initialization code written for you. Once you get used to this kind of personal service, you really can't go back.

Where to get reliable solutions

Don't search randomly on Baidu, there are too many outdated hydrology. Go directly to the official websites of major chip manufacturers, such as those of TI, MPS, and ROHM, screen them with the product selection tool, download the official evaluation board schematics, and copy them. The domestic Xiangfengyao official website also has a complete steering gear reference design, and the BOM and PCB files are fully open.

When searching, use the correct keywords: steering gear driver IC, DC motor driver, brush motor pre-driver. When you see the two functions of "integrated current detection" and "PWM control interface", they are basically what you want. Download the user manual and look directly at Section 7.3 "Typical Application Circuit". That diagram is absolutely reliable.

What kind of steering gear are used in the products you are making recently? Is it a standard PWM interface or a smart servo with feedback? Welcome to chat about your selection experience in the comment area, and give it a like so that more friends who make products can see this article.