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ADC CURRENT SCLAING IN 28335 DSP PROCESSOR

Joseph Peter
Intellectual 665 points


hi sir

i am using ti 28335 dsp processor.with max 3.3 v...i am having stator currents of 0-5v range from intelligent power module sensors...i want to scale it down to 3.3 v before giving into dsp processor 12 BIT adc pins.How can i do the same..wether the below conversion ll do the same?

ADCINA0=ADCRegs.Result0>>4;

ADCINB0=ADCRegs.Result1>>4;

Ia=ADCINA0*4096/3.3;
Ib=ADCINB0*4096/3.3;

Can you suggest me on the adc conversions?

  • 0
    TI__Genius 15311 points

    Hi Joseph,

    The ADC input range of the F28335 is limited to 0-3V, you need to scale the analog voltage to be within this range.  Any voltage between 3V and 3.3V will saturate the conversion results at 4095.  Voltages above VDDA+0.3V can cause start to adversely affect other channels' conversions.  Performance cannot be guaranteed when operating outside the Recommended Operating Conditions and certainly 5V is even beyond the Absolute Maximum Ratings and could easily cause permanent damage to the device.

    Since it is recommended to buffer the ADC input, perhaps you can use an opamp to scale down the voltage to the proper range.

    For more information you can review the above mentioned and ADC Electrical Characteristics sections of the datasheet as well as the ADC reference guide.

    Regards,

    Joe

  • 0 in reply to Joe Prushing
    Intellectual 665 points
    hi thanks for the response..
    can u give me idea on scaling factors used in adc for 3.3 v 28335 dsp processor.when i am using adc i ll get a digital value rt...can i use that value for nfurther calulations in isr....or should i back convert that digital value to voltage?
  • 0 in reply to Joseph Peter
    TI__Genius 15311 points

    The equations in your original post are not quite right.  The formula to calculate the ideal digital conversion from an analog voltage is specified in the datasheet in the section titled Analog-to-Digital Converter (ADC) Module (it is also in the aforementioned ADC user guide).

    As to whether to use the digital conversions directly in your calculations or convert them back to voltage, I think that is user preference and application specific, but I would assume in most situations, keeping it digital is a lot easier to deal with than converting to a floating point voltage value.