Multifunctional MEMS sensor monitor
iC Haus' controller monitors the flow, gas, pressure and sensor temperature using an energised heating resistor
iC Haus' iC-HO device is a universal sensor interface.
It has a configurable signal conditioner, a fast analogue/digital converter, configurable current sources, temperature drift compensation, digital sensor configuration, an SPI µC interface, adjustable linearisation, and a ratiometric, differential analogue output.
All of these functions are housed on a monolithic chip in a QFN32 package measuring 5 mm x 5 mm.
Resistive mass airflow sensors are driven by iC-HO using two identical reference currents so that the voltage difference conditioned by the programmable amplifier (PGA) can be measured and processed in a digitised form. A temperature control unit is also integrated into the chip.
With gas sensors, a variable tracking controller for two temperatures with a configurable temporal sequence is used. Differential, synchronous recording of the sensor resistance can be configured.
The company says with this controller, splitting the heating resistor and sensor resistor on a sensor MEMS element as iC-HO electrically separates the heating and measurement units.
With pressure sensors, for example, iC-HO provides differential measurement on a resistor measuring bridge as a half or full bridge. By performing an additional measurement the sensor temperature curve can be suitably compensated for.
It is also possible to supply the measuring bridge using a constant current source in place of a voltage.
For flow and gas sensor applications a heating system with a control circuit is also required in addition to the sensor conditioning unit. An on-chip heating controller drives a sensor heating resistor through additional differential sensor inputs and a digital PI controller with D/A conversion. The PI controller can exercise both relative and absolute control over the temperature. A maximum heating current can be specified to protect the external MEMS sensors.
Gain and offset correction of the programmable amplifier (PGA) can be automatically tracked for the purpose of sensor temperature compensation. The fast, 11-bit A/D converter can either process the measurement values directly or as the difference between two conversions.
The measurement values are output through a ratiometric, differential analogue output. Alternatively, the SPI interface implemented for chip configuration can be used to scan the measurement value and system state through a microcontroller.
Error states and error thresholds can be defined to monitor and diagnose the sensor and chip. These are output through an open collector switching output or the SPI interface.
iC-HO has an internal reference voltage and can output internal analogue signals and the bias current to standard signal pins for calibration.
iC-HO operates from 4.5 V to 5.5 V within a temperature range of -25°C to +104°C. At 5 mm x 5 mm x 1 mm the 32-pin QFN package is extremely compact and has a very good heat dissipation.
The design-in process is supported by ready-to-operate demo boards and software for evaluation with a PC.
