SNOSDD8 December   2022 LM7480

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 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
    6. 7.6 Switching Characteristics
    7. 7.7 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Charge Pump
      2. 9.3.2 Dual Gate Control (DGATE, HGATE)
        1. 9.3.2.1 Reverse Battery Protection (A, C, DGATE)
        2. 9.3.2.2 Load Disconnect Switch Control (HGATE, OUT)
      3. 9.3.3 Overvoltage Protection and Battery Voltage Sensing (VSNS, SW, OV)
      4. 9.3.4 Low Iq Shutdown and Under Voltage Lockout (EN/UVLO)
    4. 9.4 Device Functional Modes
    5. 9.5 Application Examples
      1. 9.5.1 Redundant Supply OR-ing with Inrush Current Limiting, Overvoltage Protection and ON/OFF Control
      2. 9.5.2 Ideal Diode With Unsuppressed Load Dump Protection
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical 12-V Reverse Battery Protection Application
      1. 10.2.1 Design Requirements for 12-V Battery Protection
      2. 10.2.2 Automotive Reverse Battery Protection
      3. 10.2.3 Detailed Design Procedure
        1. 10.2.3.1 Design Considerations
        2. 10.2.3.2 Charge Pump Capacitance VCAP
        3. 10.2.3.3 Input and Output Capacitance
        4. 10.2.3.4 Hold-Up Capacitance
        5. 10.2.3.5 Overvoltage Protection and Battery Monitor
      4. 10.2.4 MOSFET Selection: Blocking MOSFET Q1
      5. 10.2.5 MOSFET Selection: Hot-Swap MOSFET Q2
      6. 10.2.6 TVS Selection
      7. 10.2.7 Application Curves
    3. 10.3 200-V Unsuppressed Load Dump Protection Application
      1. 10.3.1 Design Requirements for 200-V Unsuppressed Load Dump Protection
      2. 10.3.2 Design Procedure
        1. 10.3.2.1 Boost Converter Components (C2, C3, L1)
        2. 10.3.2.2 Input and Output Capacitance
        3. 10.3.2.3 VS Capacitance, Resistor, and Zener Clamp
        4. 10.3.2.4 Overvoltage Protection and Output Clamp
        5. 10.3.2.5 MOSFET Q1 Selection
        6. 10.3.2.6 Input TVS Selection
        7. 10.3.2.7 MOSFET Q2 Selection
      3. 10.3.3 Application Curves
    4. 10.4 Do's and Don'ts
    5. 10.5 Power Supply Recommendations
      1. 10.5.1 Transient Protection
      2. 10.5.2 TVS Selection for 12-V Battery Systems
      3. 10.5.3 TVS Selection for 24-V Battery Systems
    6. 10.6 Layout
      1. 10.6.1 Layout Guidelines
      2. 10.6.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

10.5.2 TVS Selection for 12-V Battery Systems

In selecting the TVS, important specifications are breakdown voltage and clamping voltage. The breakdown voltage of the TVS+ should be higher than 24-V jump start voltage and 35-V suppressed load dump voltage and less than the maximum ratings of LM7480 (65 V). The breakdown voltage of TVS- should be beyond than maximum reverse battery voltage –16 V, so that the TVS- is not damaged due to long time exposure to reverse connected battery.

Clamping voltage is the voltage the TVS diode clamps in high current pulse situations and this voltage is much higher than the breakdown voltage. In the case of an ISO 7637-2 pulse 1, the input voltage goes up to –150 V with a generator impedance of 10 Ω. This translates to 15 A flowing through the TVS - and the voltage across the TVS would be close to its clamping voltage.

The next criterion is that the absolute maximum rating of cathode to anode voltage of the LM7480 (85 V) and the maximum VDS rating MOSFET are not exceeded. In the design example, 60-V rated MOSFET is chosen and maximum limit on the cathode to anode voltage is 60 V.

During ISO 7637-2 pulse 1, the anode of LM7480 is pulled down by the ISO pulse, clamped by TVS- and the MOSFET Q1 is turned off quickly to prevent reverse current from discharging the bulk output capacitors. When the MOSFET turns off, the cathode to anode voltage seen is equal to (TVS Clamping voltage + Output capacitor voltage). If the maximum voltage on output capacitor is 16 V (maximum battery voltage), then the clamping voltage of the TVS- should not exceed, (60 V – 16) V = –44 V.

The SMBJ33CA TVS diode can be used for 12-V battery protection application. The breakdown voltage of 36.7 V meets the jump start, load dump requirements on the positive side and 16-V reverse battery connection on the negative side. During ISO 7637-2 pulse 1 test, the SMBJ33CA clamps at –44 V with 12 A of peak surge current as shown in and it meets the clamping voltage ≤ 44 V.

SMBJ series of TVS' are rated up to 600-W peak pulse power levels and are sufficient for ISO 7637-2 pulses.