SLLSE26E november   2010  – august 2023 ISO35T

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
    1.     Pin 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: Driver
    10. 6.10 Electrical Characteristics: Receiver
    11. 6.11 Supply Current
    12. 6.12 Transformer Driver Characteristics
    13. 6.13 Switching Characteristics: Driver
    14. 6.14 Switching Characteristics: Receiver
    15. 6.15 Insulation Characteristics Curves
    16. 6.16 Typical Characteristics
  8. 7 Parameter Measurement Information
    1.     26
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Device Functional Modes
      1. 8.3.1 Device I/O Schematics
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Transient Voltages
      3. 9.2.3 Application Curve
  11. 10Power Supply Recommendations
  12. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  13. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  14. 13Mechanical, Packaging, and Orderable Information

9.2.2.1 Transient Voltages

Isolation of a circuit insulates it from other circuits and earth so that noise develops across the insulation rather than circuit components. The most common noise threat to data-line circuits is voltage surges or electrical fast transients that occur after installation and the transient ratings of ISO35T are sufficient for all but the most severe installations. However, some equipment manufacturers use their ESD generators to test transient susceptibility of their equipment and can easily exceed insulation ratings. ESD generators simulate static discharges that may occur during device or equipment handling with low-energy but very high voltage transients.

Figure 9-3 models the ISO35T bus IO connected to a noise generator. CIN and RIN is the device and any other stray or added capacitance or resistance across the A or B pin to GND2, CISO and RISO is the capacitance and resistance between GND1 and GND2 of ISO35T plus those of any other insulation (transformer, etc.), and we assume stray inductance negligible. From this model, the voltage at the isolated bus return is shown in Equation 1 and will always be less than 16 V from VN.

Equation 1. GUID-2ED15C37-38A1-4995-A0BB-9A5902A575EA-low.gif

If ISO35T is tested as a stand-alone device, RIN= 6 × 104Ω, CIN= 16 × 10-12 F, RISO= 109Ω and CISO= 10-12 F.

In Figure 9-3 the resistor ratio determines the voltage ratio at low frequency and it is the inverse capacitance ratio at high frequency. In the stand-alone case and for low frequency, use Equation 2, or essentially all noise appears across the barrier.

Equation 2. GUID-C5E8BF24-2C76-4FCE-813B-93F346DC5C43-low.gif

At very high frequency, Equation 3 is true and 94% of VN appears across the barrier.

Equation 3. GUID-742436B4-B756-4D7B-9BA5-675EF9A8410B-low.gif

As long as RISO is greater than RIN and CISO is less than CIN, most of transient noise appears across the isolation barrier, as it should.

We recommend the reader not test equipment transient susceptibility with ESD generators or consider product claims of ESD ratings above the barrier transient ratings of an isolated interface. ESD is best managed through recessing or covering connector pins in a conductive connector shell and installer training.

GUID-B63BE4C0-54E2-4D19-B9EA-8F29B4A66412-low.gif Figure 9-3 Noise Model