Maria Montero

Innovative Isolated ICs from Silicon Labs promise precision and …

Silicon Labs announced a new family of isolated analog amplifiers, voltage sensors, and delta-sigma modulator devices at APEC2019. The Si89xx family of products offers voltage, current and package options for electrical engineers with a focus on power electronics.

Power control systems require an accurate 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 at 5V or less potential difference, while most industrial motors operate at 240V or more. To measure the high voltage present in a motor with the low voltage present in the microcontroller requires a bit of engineering. Standard industrial design best practice is to galvanically isolate high voltage circuits from low voltage circuits, meaning that there is no possible electrical path that an electron can take from the high voltage side to the low voltage side of the circuit.

Future-oriented design

In the past, engineers have used transformers, optocouplers, and hall effect sensors to measure high-voltage lines with low-voltage sensors. Silicon Labs, however, chose to use integrated capacitors in its ICs to make the connections within its CMOS ICs.

You might ask why an engineer would choose a capacitive-based CMOS solution over an optocoupler solution. The answer is that all optical devices change throughout their lives, as Rudye McGlothlin of Silicon Labs points out in an APEC interview. “You don’t design for how an optocoupler works now, you design for how it’s going to work five years from now.” Electronic efficiency varies a lot with time, temperature and voltage, “he says.

“In some isolation technologies, electromagnetic. [emissions] they are a big problem. But our implementation is based on capacitives, a really small capacitance with differential signaling, our EMI performance is really good, “says McGlothlin.

Next-generation sensors and applications

The third generation of sensors recently announced by Silicon Labs has a working voltage of 1414 V and can withstand bipolar surges of up to 13 kV. Devices in this family typically have offset errors as low as ± 40 µV, ± 0.1% gain error, offset deviation as low as ± 0.15 µV / ° C, drift gain as low as -6 ppm / ° C , and SNR up to 90 dB.

The Si89xx family. Image courtesy of Silicon Labs.

Industrial applications include industrial and renewable energy inverters; AC, Brushless and DC Drives and Controls; variable speed motor control; and isolated and switched mode power supplies.

Automotive applications include battery management, industrial data acquisition, and industrial sensor interfaces.

Products on the 89xx line.

Si892x isolated analog amplifiers optimized for leakage current detection.

Functional block diagram from SiLabs 8920 datasheet.

Si8931 / 2 isolated analog amplifiers optimized for general purpose voltage sensing.

Functional block diagram from Si8931 / 2 data sheet.

Si8935 / 6/7 isolated DSM devices optimized for voltage sensing