SBASAA6A August   2021  – December 2021 AMC1350

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

8.2.2 Detailed Design Procedure

This discussion covers the 230-VRMS example. The procedure for calculating the resistive divider for the 120-VRMS 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 AMC1350, 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 AMC1350 (that is, +5 V). RSNSEFF is calculated as RSNSEFF = VFSR / (VPeak – VFSR) × RTOP where RTOP is the total value of the 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 120-VRMS LINE VOLTAGE 230-VRMS LINE VOLTAGE
Peak voltage 190 V 360 V
Unit resistor value, RTOP 634 kΩ 715 kΩ
Number of unit resistors in RTOP 3 5
Sense resistor value, RSNS 53.6 kΩ 52.3 kΩ
Total resistance value (RTOP + RSNS) 1953.4 kΩ 3625.2 kΩ
Resulting current through resistive divider, ICROSS 97.3 μA 99.3 μA
Resulting full-scale voltage drop across sense resistor RSNS 4.993 V 4.982 V
Peak power dissipated in RTOP unit resistor 6 mW 7.1 mW
Total peak power dissipated in resistive divider 18.5 mW 35.7 mW