SBASAQ5A june   2023  – august 2023 AMC3311

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Power Ratings
    6. 6.6  Insulation Specifications
    7. 6.7  Safety-Related Certifications
    8. 6.8  Safety Limiting Values
    9. 6.9  Electrical Characteristics
    10. 6.10 Switching Characteristics
    11. 6.11 Timing Diagram
    12. 6.12 Insulation Characteristics Curves
    13. 6.13 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Analog Input
      2. 7.3.2 Isolation Channel Signal Transmission
      3. 7.3.3 Analog Output
      4. 7.3.4 Isolated DC/DC Converter
      5. 7.3.5 Diagnostic Output and Fail-Safe Behavior
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Filter Design
        2. 8.2.2.2 Differential to Single-Ended Output Conversion
      3. 8.2.3 Application Curve
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Device Nomenclature
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2 Detailed Design Procedure

The 100-μA, cross-current requirement at the maximum DC link voltage (400 V) determines that the total impedance of the resistive divider is 4 MΩ. The impedance of the resistive divider is dominated by the top portion (shown exemplary as RX1 and RX2 in Figure 8-1) and the voltage drop across RSNS1 and RSNS2 can be neglected for a moment. The maximum allowed voltage drop per unit resistor is specified as 75 V; therefore, the minimum number of unit resistors in the top portion of the resistive divider is 400 V / 75 V = 6. The calculated unit value is 4 MΩ / 6 = 667 kΩ and the next closest value from the E96 series is 665 kΩ.

The total sense resistor (RSNS = RSNS1 + RSNS2) is sized such that the voltage drop across the resistor at the maximum DC link voltage (400 V) equals the linear full-scale range input voltage (VFSR) of the AMC3311, which is 2 V. This resistance is calculated as RSNS = VFSR / (VDC-link, max – VFSR) × RTOP, where RTOP is the total value of the top resistor string (6 × 665 kΩ = 3990 kΩ). RSNS is calculated as 20.05 kΩ and split into two equal resistors (RSNS1 and RSNS2) of 10 kΩ each, a value from the E96 series.

The isolated comparator senses the voltage drop across RSNS2. At the specified DC link overvoltage of 450 V, the voltage drop across RSNS2 is RSNS2 / (RTOP + RSNS1 + RSNS2) × VDC-link and equals 1.12 V. This value is the trip threshold value, VREF. The trip threshold is set by the resistor RREF and is calculated as (1.12 V – 4 mV) / 100 μA = 11.2 kΩ. A value of 11 kΩ is selected from the E96 series, resulting in a slightly lower reference voltage of 1.1 V. The 4-mV value subtracted from VREF is related to the hysteresis of the isolated comparator on the rising edge of VIN. 100 μA is the value of the internal current source connected to the REF pin of the AMC23C11. For a detailed calculation of the trip threshold, see the AMC23C11 data sheet. The resulting overvoltage detection threshold is (VREF + 4 mV) / RSNS1 × (RTOP + RSNS1 + RSNS2), or 443 V.

The reference of the AMC23C11 comparator requires a minimum headroom to VDD1 of 1.4 V. The minimum supply voltage (VDD1) to the isolated comparator is in the minimum output voltage of the AMC3311 high-side LDO (VHLDO_OUT), which equals 3 V. Therefore, the reference operates at a minimum headroom of 3 V – 1.1 V = 1.9 V and satisfies the design requirements.

Table 8-2 summarizes the design parameters for this application.

Table 8-2 Design Summary
PARAMETER VALUE
Unit resistor value, RX 665 kΩ
Number of unit resistors 6
Sense resistor values (RSNS1 and RSNS2) 10 kΩ
Resulting current through resistive divider (ICROSS at 400 V) 99.8 μA
Resulting full-scale voltage drop across sense resistor (RSNS1 + RSNS2) 1.995 V
Total power dissipated in resistive divider 39.9 mW
Power dissipated in unit resistor RX 6.6 mW
AMC23C11 reference resistor value, RREF 11 kΩ
Resulting overvoltage detection threshold 443 V