SBASAB4 December   2021 AMC1351-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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
  7. 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. 7.4 Device Functional Modes
  8. 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 What To Do and What Not To Do
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8.2.2 Detailed Design Procedure

This discussion covers the 360-VDC example. The procedure for calculating the resistive divider for the 190-VDC use case is identical.

The 100-μA, cross-current requirement at peak input voltage (360 V) determines that the total impedance of the resistive divider is 3.6 MΩ. The impedance of the resistive divider is dominated by the top resistors (shown exemplary as R1 and R2 in Figure 8-1) and the voltage drop across RSNS can be neglected for a short time. The maximum allowed voltage drop per unit resistor is specified as 75 V; therefore, the total minimum number of unit resistors in the top portion of the resistive divider is 360 V / 75 V = 5. The calculated unit value is 3.6 MΩ / 5 = 720 kΩ and the next closest value from the E96 series is 715 kΩ.

The effective sense resistor value RSNSEFF is the parallel combination of the external resistor RSNS and the input impedance of the AMC1351-Q1, RIN. RSNSEFF is sized such that the voltage drop across the impedance at maximum input voltage (360 V) equals the linear full-scale input voltage (VFSR) of the AMC1351-Q1 (that is, 5 V). RSNSEFF is calculated as RSNSEFF = VFSR / (VPeak – VFSR) × RTOP, where RTOP is the total value of top resistor string (5 × 715 kΩ = 3575 kΩ). The resulting value for RSNSEFF is 9.96 kΩ. In a final step, RSNS is calculated as RSNS = RIN × RSNSEFF / (RIN – RSNSEFF). With RIN = 1.25 MΩ (typical), RSNS equals 52.47 kΩ and the next closest value from the E96 series is 52.3 kΩ.

Table 8-2 summarizes the design of the resistive divider.

Table 8-2 Resistor Value Examples
PARAMETER 190-VDC LINE VOLTAGE 360-VDC LINE VOLTAGE
Unit resistor value (RTOP) 634 kΩ 715 kΩ
Number of unit resistors in RTOP 3 5
Sense resistor value (RSNS) 51.1 kΩ 49.9 kΩ
Total resistance value (RTOP + RSNS) 1953.1 kΩ 3624.9 kΩ
Resulting current through resistive divider (ICROSS) 97.3 μA 99.3 μA
Resulting full-scale voltage drop across sense resistor RSNS 4.971 V 4.956 V
Peak power dissipated in RTOP unit resistors 6 mW 7.1 mW
Total peak power dissipated in resistive divider 18.5 mW 35.8 mW