Position encoding in battery-powered electronics: Page 2 of 5

October 09, 2014 //By Jonas Kupp and David Lin
Position encoding in battery-powered electronics
Jonas Kupp and David Lin consider the benefits of position encoding in battery-powered electronics.
components. The magnetic field is generated by a magnet that rotates above the chip. By using three-phase sampling, only 3 Hall sensors are required instead of the usual 4, reducing current consumption by approximately 25%.

Always On

To allow permanent battery-powered operation, an integrated 1-chip ULP design must be able to completely turn itself on and off. Figure 1 shows such ULP architecture based on the iC-TW11 from iC-Haus. This device has been developed specifically for battery-powered applications, which require highly integrated energy saving and precise position measurement. It is connected to a central microcontroller—preferably also a ULP design—via an SPI interface. Position measurement and sampling of the Hall sensors only occurs when it is actually required.

There are no unnecessary measuring cycles which would waste energy from the battery. All circuit elements not needed are turned off after measurement and conversion is finished. The sampling of the Hall sensors, the downstream amplifier circuit with control and automatic calibration, as well as the interpolation for the angle measurement is designed to be fast and energy-saving at the same time. That way an average current of less than 3 µA at a sampling rate of 10 Hz and a resolution of 10 bits is achieved.

In the automatically activated standby mode between position measurements, current consumption of the complete 1-chip Hall encoder is only 100 nA maximum. The supply current as a function of the selected sampling frequency is shown in figure 2. The interfaces to the outside world operate at 3.3 V or 1.8 V. Therefore, no level shifter is needed for interfacing to a ULP microcontroller which uses a lower supply voltage.

For position measurement, short measuring times are desired, which means a low latency time between the beginning of the measurement and when the result is available. In order for the ULP microcontroller to be able to switch to standby mode after a position measurement, an interrupt output

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