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sampling drv201

Other Parts Discussed in Thread: DRV201, TS3A44159

Hi

I needed digital driver that can give me sin wave using I2C commands.

I used drv201 and a mux ts3a44159 with the mux I switch the legs of the DRV output when the sin is negative and this is how I get full sin between (-1 to 1 V). 

I want to sample the output from the DRV 201.

the problem is that I can only measure positive difference (negative will be 0) in my a/d .

I wanted to use an unit op amp to calculate the difference between the drv+mux output and to add a bias to the result so I would be able to sample it (I want to see the output sin with bias).

how can I do it in the easiest way? (I cant add bias to one of the coil sided because I will force this voltage on one of the coils legs and this will change the output)

thanks  in advanced,

  • Hi, It is better to have your schematic for discussion. Driving a motor or pure resister to get sin voltage? How is your ground connection?

    Thanks

  • Hi

    the schematics is simple. I connected I sink to com1 of the mux - NC1 and NO2 of the mux to one side of the coil.

    I connected I source to com2 of the mux - NC2 and NO1 of the mux to the other side of the coil.

    the drv and the mux have the same 3.3V voltage and the same ground.

    the sda and sdl are connected to the controller with 4.7K resistors.

    the mux in1-2 is also connected to the controller.

    I am flowing the current from the DRV and mux in a coil -(17 ohm and 70uH). the circuit is working and I can see the sin wave using a scope. the problem is how to sens it using A/D (without negative option). I thought using unit op amp to get the difference between the coil sides and add  bias to it and then sample it. how can I do it without changing the sin signal on the coil?

    thanks,

     

  • So, if I get it correctly, you want to sample the whole sine wave with your unit gain Opamp and ADC (both single ground) circuit.

    Is there any connection between the (DRV+MUX)'s ground and the (OPAMP+ADC)'s ground. Maybe they are the same ground in your system unless you have two isolated powers.

    if this two parts are really isolated, you can use a simple unit gain OPAMP(two ends of the coil go to - and + input) with 1/2 ADC VREF bias circuit (a voltage divider form a 1/2 VREF bias to +input) to shift the +/- sine to the single ground and feed to ADC.

    if the two section's grounds are the same, you need note that the sink and source all has it's voltage level within the GND to 3.3V. So you need an adjustable bias to the OPAMP stage to tune the output swing within the ADC input range.

  • Hi

    thank you for your answer.

    as for your question the gnd of the drv+mux and the op amp+adc are all the same.

    I know I need adjustable bias to the op amp but how do I do it? 

    can you propose a  circuit or component for this?

    Regards,

  • Hi,

    You can refer to any material related to OPAMP. I give you one just for your reference.

    Regards,

  • Hi

    thanks,

    I havent tried this exactly but I have tried thing similar to this.

    the problem I had and I think it will also be here is that the vcc that force one of the op amp legs is connected to the DRV (through the mux) and will force voltage on one of its outputs. this make the DRV stop working and ruins the signal.

    but I have tried it without the resistor before the opamp "+" so maybe that was my problem (not sure).

    I will try it with 1K resistors and see what happens next week.

    thank you very much.

      

  • Hello Or,

    This may or may not be helpful.  I was trying to do a similar thing of converting a bipolar signal to a unipolar one.  You can read this post and use the excel spreadsheet to suit your input and out requirements.

    http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/214907/760047.aspx#760047

    Thanks,

  • thank you very much