i am running a bldc motor Infineon TLE9879 chip. Now i want to measure the current flowing through the motor. so i use the current sense amplifier where the motor current is converted to a voltage by means of a shunt resistor RSH(0.005 ohm).

I want to measure current from 0.1amp to 3Amps which gives the voltage drop at RSH (0.1*0.005=0.0005volts to 3*0.005=0.015volts). Considering 5V reference voltage of ADC I will not be able to get a good number for the above voltage drop. Also with the maximum gain of CSA the output is still negligible. The data sheet says you need to do linear calibration but how to do it for the entire current range? If anyone has experience with CSA please share how to do it? Attachment CSAdatasheet

I am adding some new information here. Actually, when I checked the current in one of the phases of the bldc motor it appears like the following enter image description here Its amplitude increases as the load on the motor increases.

I was doing a mistake of reading the ADC value in every 100ms without any synchronisation with the actual current waveform. That's why the ADC value always shows the offset value of the opamp. I think I need to measure the RMS value of the voltage developed at the shunt. Please let me know if I am correct!!!

  • \$\begingroup\$ anyone know what exactly happens in CSA? \$\endgroup\$
    – litun bls
    Mar 12 '18 at 20:16
  • \$\begingroup\$ Please use engineering prefixes. \$\endgroup\$
    – winny
    Mar 12 '18 at 21:11

The CSA has programmable gains 10, 20, 40, 60. So if you used gain of 60 the input to the ADC would be 0.9V at 3 amps. The data sheet shows a calibration unit. The user's manual explains how to use it.

  • \$\begingroup\$ can you tell me where it is mentioned calibration of the current sense amplifier? Current sense amplifier comes in ADC1. \$\endgroup\$
    – litun bls
    Mar 13 '18 at 4:57
  • \$\begingroup\$ Here my task is to stop the motor as soon as the motor is running on no-load. I could see the no-load current from my DC power supply and it remains between 0.4 to 0.6 amp. \$\endgroup\$
    – litun bls
    Mar 13 '18 at 5:00
  • \$\begingroup\$ Click on the user's manual link I provided and search for calibration. \$\endgroup\$
    – EE_socal
    Mar 13 '18 at 15:43
  • \$\begingroup\$ i have seen all calibration in the datasheet. But if you understood my question, please answer. \$\endgroup\$
    – litun bls
    Mar 13 '18 at 18:36
  • \$\begingroup\$ how it is possible to measure 0.1A to 3A current with 5v reference voltage for ADC \$\endgroup\$
    – litun bls
    Mar 13 '18 at 18:41

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