SBAA666 February   2025 AMC0106M05 , AMC0106M25

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Design Challenges
  6. 3Design Approach
    1. 3.1 AMC0106Mxx Functionally Isolated Modulators
    2. 3.2 Circuit Design and Layout
    3. 3.3 Sinc3 Filter Design
  7. 4Test and Validation
    1. 4.1 Test Setup
    2. 4.2 Digital Interface
    3. 4.3 DC Accuracy, Noise, and Effective Number of Bits
    4. 4.4 PWM Rejection
      1. 4.4.1 DC Phase Current Measurement Over One PWM Cycle
      2. 4.4.2 AC Phase Current Measurement at 100kHz PWM
    5. 4.5 Bootstrap Supply Validation and AVDD Ripple Rejection Tests
      1. 4.5.1 LMG2100R044 Bootstrap Supply With Low Voltage-Ripple
      2. 4.5.2 Discrete Bootstrap Supply With High Voltage-Ripple
  8. 5Summary
  9. 6References

3 Design Approach

Several designs exist for in-phase current sensing in space constrained applications where a small form factor and low height are critical. In-package Hall sensors, shunts with non-isolated amplifiers, and shunts with isolated amplifiers or isolated delta-sigma modulators are just a few of them.

Shunt-based current sensing with a delta-sigma modulator offers the highest measurement resolution and is the method of choice for high-performance motor drives. The digital interface to the microcontroller offers the additional benefit of high EMC immunity. For <60V operation functional isolation is sufficient. Figure 3-1 shows a simplified block diagram of a shunt, a 8-pin, functionally isolated, modulator, and a microcontroller connected to the delta-sigma modulator through a two-wire interface for clock and data. The microcontroller contains a digital low-pass filter, such as a sync3 filter, that also converts the 1-bit data stream at a high sampling rate into a higher-bit data word at a lower rate (decimation).

Isolated Phase Current Sense Subsystem with MCU Integrated Sync Filter Figure 3-1 Isolated Phase Current Sense Subsystem with MCU Integrated Sync Filter