SPRACT7 August   2020 TMS320F280021 , TMS320F280021-Q1 , TMS320F280023 , TMS320F280023-Q1 , TMS320F280023C , TMS320F280025 , TMS320F280025-Q1 , TMS320F280025C , TMS320F280025C-Q1 , TMS320F280040-Q1 , TMS320F280040C-Q1 , TMS320F280041 , TMS320F280041-Q1 , TMS320F280041C , TMS320F280041C-Q1 , TMS320F280045 , TMS320F280048-Q1 , TMS320F280048C-Q1 , TMS320F280049 , TMS320F280049-Q1 , TMS320F280049C , TMS320F280049C-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Fundamental Theories of FOC and Current Measurement
    1. 2.1 Basic Theory of FOC
    2. 2.2 Current Sensing Technique
      1. 2.2.1 Low-Side Current Measurement
        1. 2.2.1.1 Three-Shunt Current Sensing
        2. 2.2.1.2 Dual-Shunt Current Sensing
        3. 2.2.1.3 Single-Shunt Current Sensing
  5. 3Implementation of Single-Shunt Phase Current Reconstruction
    1. 3.1 Duty Cycle Compensation
    2. 3.2 PWM Phase Shift Compensation
    3. 3.3 Current Reconstruction
  6. 4Sensorless FOC With Single-Shunt Measurement
  7. 5Hardware Consideration for Single-Shunt Current Sensing
    1. 5.1 Slew Rate
    2. 5.2 Current Sensing Circuit
  8. 6Test Results
  9. 7Summary
  10. 8References

5.1 Slew Rate

A rising time of operational amplifier directly affect the current sensing delay as shown in Figure 2-11. So, when using the single-shunt technique, the slew rate parameter of op amp should be carefully considered. If the settling time of feedback signal and ADC sampling time are fixed parameters, the op-amp slew rate is important parameter to minimize duty cycle to be phase shifted. Generally, a slew rate of 10V/μs or more is recommended for single-shunt measurement.

F28004x, which is one of C2000 Generation 3 MCU in entry to middle performance portfolio, has Programmable Gain Amplifier (PGA) for amplifying an input voltage. The integrated PGA helps to reduce cost and design effort for many control applications that require external, standalone amplifier. Table 5-1 shows that the slew rate of the integrated PGA in F28004x is high enough for single-shunt measurement under all gain setting conditions.

Table 5-1 F28004x PGA Slew Rate
Parameter Test Conditions Typical Value
Slew Rate Gain = 3 20 V/us
Gain = 6 37 V/us
Gain = 12 73 V/us
Gain = 24 98 V/us