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Incremental encoder IC eyes small motors

Posted: 18 Jul 2011 ?? ?Print Version ?Bookmark and Share

Keywords:optical sensor? incremental encoder? encoder IC?

The iC-LTA and the iC-PT series of optical sensors from iC-Haus GmbH boast a supply of incremental and commutation signals in the smallest possible design space. They are based on a flat optoQFN that is 0.9mm thick with an ultrathin glass lid.

According to iC-Hause, the optimised phased array structure of the photochips means that a minimal scanning area of just 1.9 x 3.1mm is enough to generate 2,500 pulses from a code disc measuring only 26mm across, for example.

iC-PT sensors and measurement standards for diameters of 26mm (iC-PT2613) and 33mm (iC-PT33xx) are available. iC-LTA is a functionally compatible yet unstructured photo array for specific customised design. The Hall sensors used for motor commutation to date have been replaced by three separate on-chip scanning tracks. Here, the code disc stipulates the required signal and can be easily designed to suit the required motor pole count.

The photocurrent signals are conditioned by low-noise CMOS amplifiers and can either be comparated or interpolated twice and output through 4mA push/pull drivers as indexed encoder quadrature signals. Output frequencies of up to 800kHz are permitted, enabling motors with speeds of up to 20,000rpm to be controlled (at 2,500 pulses). Analog test signals can be activated for assembly and alignment.

The small sampling area and a high sensitivity help to reduce the amount of power needed for the obligatory LED; a few milliamps of operating current are sufficient. This improves the expected lifetime of the LED, especially if the motor has high operating temperatures. The iC-LTA and iC-PT devices control the LED themselves and also compensate for fluctuations in the operating temperature range of -40C C120C.

Using the latest encoder LEDs, such as iC-TL85 or iC-SD85, for example, the system current consumption is ca. 12mA, iC-Haus said. A supply voltage starting at just 3.5V is enough and enables an external polarity protection circuit and voltage regulator to be added if required when the device is operated on 5V.

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