SLVUBU3A April   2020  – October 2020 LM7480-Q1

 

  1.   Trademarks
  2. 1Introduction
    1. 1.1 Features
    2. 1.2 Applications
  3. 2Description
    1. 2.1  Input Power and Load (J1/J3 and J2/J4):
    2. 2.2  Enable Control (J5):
    3. 2.3  Over Voltage Protection (J6):
    4. 2.4  Input Voltage Monitor (J8 and VIN_MON):
    5. 2.5  Two back-back connected MOSFETs (Q1/Q3 and Q2/Q4):
    6. 2.6  Output slew rate control (R2 and C2):
    7. 2.7  Output Schottky Diode (D2) and LED indication:
    8. 2.8  TVS selection for 12-V battery protection:
    9. 2.9  TVS selection for 24-V battery protection:
    10. 2.10 Test Points:
  4. 3Schematic
  5. 4Test Equipment Requirements
    1. 4.1 Power Supplies
    2. 4.2 Meters
    3. 4.3 Oscilloscope
    4. 4.4 Loads
  6. 5Test Setup and Results
    1. 5.1 Initial Setup
    2. 5.2 Power up
    3. 5.3 Over Voltage Protection
    4. 5.4 Enable Control
    5. 5.5 Hot-plug and Disable using EN
    6. 5.6 Inrush Current Control
    7. 5.7 Load Response
  7. 6Board Layout and Bill of Materials
    1. 6.1 Board Layout
    2. 6.2 Bill of Materials
  8. 7Revision History

5.2 Power up

To verify the startup behavior, connect the oscilloscope to the evaluation module:

  • Channel 1 - Input Voltage (Test Point Label VIN)
  • Channel 2 - Output Voltage (Test Point Label VOUT)
  • Channel 3 - DGATE Voltage (Test Point Label DGATE)
  • Channel 4 - HGATE Voltage (Test Point Label HGATE)
Set the load to 200 mA, trigger to Channel 1 rising and turn ON the power supply. Startup behavior of LM74800EVM-CD is captured in Figure 5-2.

GUID-97952C7C-9FFA-4A0A-95ED-D461A5C29F1A-low.pngFigure 5-2 Power Up: DGATE and HGATE
GUID-02DC276E-FB83-4DC7-BB5A-AC0E858B4DEB-low.pngFigure 5-3 Power Up: Charge Pump and Inrush Current

Additional startup information is captured in Figure 5-3. Channel 3 captures the charge pump voltage on VCAP pin during startup. Charge pump turns on when POR threshold on VIN is reached and builds up to 13.5 V above VIN.