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Matching analog signals

SiVa Var
Prodigy 10 points

Other Parts Discussed in Thread: TMS320F28335, CONTROLSUITE

Hi

I have a question regarding to matching two analog signals:

An analog signal from a motor drive which it can supply a signal of 0-20mA or 4-20mA should be connected to an ADC in eZdsp TMS320F28335, which the analog input is from 0.0 to 3V. Ways to match the output analog signal from motor drive with the analog input signal from DSP (ADC) are as follow:

1. the easy way is to insert a resistor with 150ohm between two signals

5826.adc.pdf

2. Use an optocoupler. In this case an optocoupler like a HCPL-788J can be used which has a 6V output voltage and then connected to a voltage divider to reach 3V. 

I want to ask if you could please help me with this problem after yours experinces working with DSPs, how can I match two analog signals?,

Looking forward to hear from you

Best Regards

Siva

  • 0
    TI__Guru 57255 points

    Siva,

    Because your shunts create a fairly low-voltage signal, I would recommend putting an opamp to add some gain (10-100) to the signal before inputting it into the ADC.  Doing this will increase your controller's accuracy.

    If you have controlSUITE installed, I would recommend taking a look at the following schematic in controlSUITE.  It is a schematic of one of our evaluation kits, the TMDSHVMTRPFCKIT which uses a F28335 or F28035 to control a motor:
    \controlSUITE\development_kits\HVMotorCtrl+PfcKit_v2.0\~HVMotorCtrl+PFC-HWdevPkg\HVMotorCtrl+PFCKit-R1.1\

    I wouldn't recommend using optos unless your application requires isolation between the controller and the motor.


    Thank you,
    Brett