Power control systems require precise and near-instantaneous measurement of current and voltage to maintain efficiency and detect faults and changes in system load.
Most of today’s integrated circuits operate with 5 V of potential difference or less, while most industrial motors operate at 240 V or greater. To measure the high voltage present in a motor with the low voltage present at the microcontroller requires a bit of engineering. The standard industry design best-practice involves galvanically isolating high-voltage circuits from low-voltage circuits, meaning there is no possible electrical path an electron can take from the high-voltage side to the low-voltage side of the circuit.
At APEC, AAC's Mark Hughes got to speak to Silicon Labs about this trend and some forward-looking IC design in their new Si89xx product family.
Forward-Looking Design: The Capacitive-Based CMOS for EMI Performance
In the past, engineers have utilized transformers, optocouplers, and hall-effect sensors to measure high-voltage lines with low-voltage sensors. Silicon Labs, however, chose to use capacitors embedded in their integrated circuits to make the connections inside their CMOS ICs. This is something the AAC team saw at APEC at ADI, as well, where capacitors are included inside the packaging of their Silent Switcher 2 regulator.
You might ask why an engineer would choose a capacitive-based CMOS solution instead of an optocoupler solution. The answer is that all optical devices change over their lifespan, as Silicon Labs' Rudye McGlothlin points out in an interview at APEC: “You don’t design for how an optocoupler works now, you design for how it is going to work five years from now. The electronic efficiency varies a great deal with time, temperature, and voltage."
“In some technologies for isolation, electromagnetic [emissions] are a big issue," he adds. "But with our implementation being capacitive-based, a really small capacitance with differential signaling, our EMI performance is actually really good."
New Generation Sensors and Applications
Silicon Labs' recently-announced third generation of sensors have a working voltage of 1414 V and can withstand bipolar surges up to 13 kV. The devices in this family typically have offset errors as low as ±40 µV, ±0.1% gain error, offset drift as low as ±0.15 µV/°C, gain drift as low as -6 ppm/°C, and SNR up to 90 dB.
The Si89xx family. Image courtesy Silicon Labs.
Industrial applications include industrial and renewable energy inverters; AC, brushless, and DC motor controls and drives; variable speed motor control; and isolated and switch-mode power supplies.
Automotive applications include battery management, industrial data acquisition, and industrial sensor interfaces.
Products in the 89xx Line
- Si892x isolated analog amplifiers optimized for shunt-current sensing
Functional Block Diagram from SiLabs Si8920 datasheet.
- Si8931/2 isolated analog amplifiers optimized for general-purpose voltage sensing.
Functional block diagram from the Si8931/2 datasheet.
- Si8935/6/7 isolated DSM devices optimized for voltage sensing
Functional block diagram from Si8935/6/7 datasheet.
- Si8941/6/7 isolated DSM devices optimized for shunt-current sensing
Functional block diagram from Si8941/6/7 datasheet.
Are you a power engineer with experience with one of these devices? Tell us about it in the comments below!