TIDUF43 August   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Terminology
    2. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 TPS1213-Q1 45V, Low IQ, Automotive High-Side Switch Controller With Low-Power Mode and Adjustable Load Wakeup Trigger
      2. 2.3.2 INA296x-Q1 AEC-Q100, –5V to 110V, Bidirectional, 1.1MHz, 8V/μs, Ultra-Precise Current-Sense Amplifier
  9. 3System Design Theory
    1. 3.1 Low-Power Mode Considerations
    2. 3.2 Precharge Circuit Considerations
    3. 3.3 Short-Circuit Protection
    4. 3.4 LM74704-Q1 Enable
    5. 3.5 Headers
      1. 3.5.1 Headers for Configuring INA296B-Q1
      2. 3.5.2 Headers for Configuring TPS1213-Q1
    6. 3.6 Software Considerations
      1. 3.6.1 Fuse Channel Definition
      2. 3.6.2 Software Functions
    7. 3.7 Optional Output TVS Diode
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Software
    3. 4.3 Test Setup
    4. 4.4 Test Results
      1. 4.4.1 State Transition
      2. 4.4.2 System IQ in Low-Power Mode
      3. 4.4.3 Precharge Test
      4. 4.4.4 Overcurrent Protection
      5. 4.4.5 PWM Overcurrent
      6. 4.4.6 Short-Circuit Protection
      7. 4.4.7 Thermal Testing
      8. 4.4.8 CISPR-25 Emissions Testing
        1. 4.4.8.1 Conducted Emissions Testing
        2. 4.4.8.2 Radiated Emissions Testing
        3. 4.4.8.3 Summary of Results
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
        1. 5.1.3.1 Layout Prints
      4. 5.1.4 Altium Project
      5. 5.1.5 Gerber Files
      6. 5.1.6 Assembly Drawings
    2. 5.2 Documentation Support
    3. 5.3 Support Resources
    4. 5.4 Trademarks
  12. 6About the Author

3.2 Precharge Circuit Considerations

To control excessive inrush current imposed by capacitive loads at start-up, an RC circuit was added on the gate driver (G2) for the low-power path. The external capacitor, C9 (Cg), reduces gate turn-on slew rate and controls the inrush current.

Equation 3 and Equation 4 were used to set the 10ms specification of the precharge period:

Equation 3. C g = C L o a d × I ( G ) I I n r u s h
Equation 4. I I n r u s h = C L o a d × V B A T T C h a r g e

where

  • I(G) = 165μA
  • VBAT represents the input voltage
  • IInrush represents the expected peak inrush current
  • TCharge represents the expected precharge time

The system enters this precharge state through the MSPM0L1306-Q1 control. At start-up, the low power path FET is slowly driven first for 15ms before the system transitions to active state.

Note: Even though C9 (Cg) can be modified to change the precharge time, the MSPM0L1306-Q1 only keeps the system in precharge mode for 15ms.