Design Support


New generations of motor control digital signal processors (DSPs) lower their supply voltages from 5V to 3.3V to offer higher performance at lower cost. Replacing traditional 5V digital control circuitry by 3.3V designs introduce no additional system cost and no significant complication in interfacing with TTL and CMOS compatible components, as well as with mixed voltage ICs such as power transistor gate drivers. Just like 5V based designs, good engineering practice should be exercised to minimize noise and EMI effects by proper component layout and PCB design when 3.3V DSP, ADC, and digital circuitry are used in a mixed signal environment, with high and low voltage analog and switching signals, such as a motor control system. In addition, software techniques such as Random PWM method can be used by special features of the Texas Instruments (TI)(tm) TMS320x24xx DSP controllers to significantly reduce noise effects caused by EMI radiation. This application report reviews designs of 3.3V DSP versus 5V DSP for low HP motor control applications. The application report first describes a scenario of a 3.3V-only motor controller indicating that for most applications, no significant issue of interfacing between 3.3V and 5V exists. Cost-effective 3.3V-5V interfacing techniques are then discussed for the situations where such interfacing is needed. On-chip 3.3V analog-to-digital converter (ADC) versus 5V ADC is also discussed. Sensitivity and noise effects in 3.3V and 5V ADC conversions are addressed. Guidelines for component layout and printed circuit board (PCB) design that can reduce system?s noise and EMI effects are summarized in the last section.