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DC bus and ADC offset compensation for IRMCF/K300 series motor control IC

Posted: 12 Jul 2007 ?? ?Print Version ?Bookmark and Share

Keywords:motor controller? ADC converter? bus voltage?

The IRMCF/K300 series motor controllers utilize an internal ADC converter for numerous important system parameters. This ADC, like all others, experiences offset in its measurements. These offsets can be amplified in measurement situations such as the DC bus voltage. With a small input range of 0-1.2V being potentially amplified into the 300-400V range, a small 10mV offset could result in DC bus measurement errors of 10V. Having such an offset may not only affect ADC performance, but rotor angle estimation, PFC, and field-weakening capability as well. These effects can be minimized through the use of an external reference for offset compensation.

IRMCF/K300 series controllers have a single ADC converter, which is multiplexed for motor current feedback, as well as DC Bus measurements. A second multiplexer is employed to provide customer configurable ADC measurements. One of these configurable 'AINx' pins can be used for offset compensation through an external reference. A separate technique employs the differential amplifiers used for current feedback to reference an external source to compensate ADC measurements. Because these inputs route to the same ADC, an offset measurement made on one channel can be applied across the system.

This application note describes how to properly and safely use the IRMCF/K300 series to measure and regulate the DC Bus voltage. Two compensation methods are outlined to improve measurement accuracy involving the ADC converter. By following these methods the ADC will allow DC bus measurements to be accurate within a few volts, rather than tens of volts. These same techniques can also be applied to non-DC bus voltage measurements for more accurate results across all of the ADC inputs.

Please view the PDF document for more information.

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