SLLS897E March   2008  – June 2015 ISO1176

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (continued)
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics: ISODE-Pin
    6. 7.6  Supply Current
    7. 7.7  Electrical Characteristics: Driver
    8. 7.8  Electrical Characteristics: Receiver
    9. 7.9  Power Dissipation Characteristics
    10. 7.10 Switching Characteristics: Driver
    11. 7.11 Switching Characteristics: Receiver
    12. 7.12 Typical Characteristics
  8. Parameter Measurement Information
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Insulation and Safety-Related Package Characteristics
      2. 9.3.2 DIN V VDE V 0884-10 Insulation Characteristics
      3. 9.3.3 IEC 60664-1 Ratings Table
      4. 9.3.4 Safety Limiting Values
      5. 9.3.5 Regulatory Information
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Transient Voltages
        2. 10.2.2.2 ISO1176 “Sticky Bit” Issue (Under Certain Conditions)
      3. 10.2.3 Application Curve
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Community Resources
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

12 Layout

12.1 Layout Guidelines

ON-chip IEC-ESD protection is good for laboratory and portable equipment but never sufficient for EFT and surge transients occurring in industrial environments. Therefore, robust and reliable bus node design requires the use of external transient protection devices. Because ESD and EFT transients have a wide frequency bandwidth from approximately 3-MHz to 3-GHz, high-frequency layout techniques must be applied during PCB design. A minimum of four layers is required to accomplish a low EMI PCB design (see Figure 35).

  • Layer stacking should be in the following order (top-to-bottom): high-speed signal layer, ground plane, power plane, and low-frequency signal layer.
  • Placing a solid ground plane next to the high-speed signal layer establishes controlled impedance for transmission line interconnects and provides an excellent low-inductance path for the return current flow.
  • Placing the power plane next to the ground plane creates additional high-frequency bypass capacitance of approximately 100 pF/in2.
  • Routing the slower speed control signals on the bottom layer allows for greater flexibility as these signal links usually have margin to tolerate discontinuities such as vias.
  • Place the protection circuitry close to the bus connector to prevent noise transients from penetrating your board.
  • Use VCC and ground planes to provide low-inductance. High-frequency currents might follow the path of least inductance and not necessarily the path of least resistance.
  • Design the protection components into the direction of the signal path. Do not force the transient currents to divert from the signal path to reach the protection device.
  • Apply 0.1-µF bypass capacitors as close as possible to the VCC-pins of transceiver, UART, and controller ICs on the board.
  • Use at least two vias for VCC and ground connections of bypass capacitors and protection devices to minimize effective via-inductance.
  • Use 1-kΩ to 10-kΩ pullup and pulldown resistors for enable lines to limit noise currents in theses lines during transient events.
  • Insert pulse-proof resistors into the A and B bus lines if the TVS clamping voltage is higher than the specified maximum voltage of the transceiver bus pins. These resistors limit the residual clamping current into the transceiver and prevent it from latching up.
  • While pure TVS protection is sufficient for surge transients up to 1 kV, higher transients require metal-oxide varistors (MOVs) which reduce the transients to a few hundred volts of clamping voltage, and transient blocking units (TBUs) that limit transient current to less than 1 mA.
  • Routing the high-speed traces on the top layer avoids the use of vias (and the introduction of their inductances) and allows for clean interconnects between the isolator and the transmitter and receiver circuits of the data link.

If an additional supply voltage plane or signal layer is needed, add a second power and ground plane system to the stack to keep it symmetrical. This makes the stack mechanically stable and prevents it from warping. Also the power and ground plane of each power system can be placed closer together, thus increasing the high-frequency bypass capacitance significantly.

NOTE

For detailed layout recommendations, see Application Note Digital Isolator Design Guide, SLLA284.

12.2 Layout Example

ISO1176 layout_sllsei6.gifFigure 35. Recommended Layer Stack