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

3.1 AMC0106Mxx Functionally Isolated Modulators

The AMC0106Mxx are precision, functionally isolated, second-order delta-sigma modulators designed for shunt-based current sensing. The M05 version supports a linear input range of ±50mV. The M25 supports a linear input range of ±250mV. The isolation barrier separates parts of the system that operate on different common-mode voltage levels. A typical application is phase current sensing in high-performance servo drives. The isolation barrier supports a working voltage up to 200VRMS / 280VDC and transient over voltages up to 570VRMS / 800VDC.

The sigma-delta modulator on the hot side receives a clock from the cold side. The modulator translates the analog input signal into a bit stream of digital ones and zeros that is synchronous to the clock. The digital bit stream is transferred back to the cold side across the galvanic isolation barrier and output on the DOUT pin. The time average of the bit stream is proportional to the analog input voltage. The block diagram of the AMC0106Mxx is shown in Figure 3-2.

AMC0106Mxx Block Diagram Figure 3-2 AMC0106Mxx Block Diagram

The modulator bit stream contains high frequency quantization noise. Therefore the bit stream is processed by a digital low-pass filter to increase measurement resolution. Many micro control units (MCUs) support delta-sigma filtering with a dedicated peripheral block, such as the Sigma-Delta Filter Module (SDFM) integrated with the C2000™ and Sitara™ microcontrollers. Alternatively, the digital filter is implemented in a field-programmable gate array (FPGA).

Isolates sigma-delta modulators have existed for many years and are an industry standard design for phase current sensing in high-performance motor drives. However, most isolated modulators are designed for high-voltage applications, are reinforced isolated, and come in packages with >8mm clearance distance. The AMC0106Mxx modulators are specifically designed for low-voltage applications, are functionally isolated, and come in a small, 2.7mm x 3.5mm lead-less package with 1mm creepage and clearance. With the small package size, the AMC0106Mxx isolated modulators enable small PCB layouts that are essential for small form-factor motor drives in robotic applications. Figure 3-3 shows a layout comparison between a AMC1306Mxx reinforced isolated modulator and an AMC0106Mxx functionally isolated modulator. The AMC0106Mxx layout consumes only half the PCB area as it's AMC1306Mxx counter part.

PCB Size Reduction AMC0106M05 versus AMC1306M05Figure 3-3 PCB Size Reduction AMC0106M05 versus AMC1306M05