SNOU187 September   2021

 

  1.   Trademarks
  2. 1Introduction
    1. 1.1 Features
    2. 1.2 Applications
  3. 2Description
    1. 2.1 Input Power and Load (J2, J6 and J3, J7):
    2. 2.2 Enable Control (J5):
    3. 2.3 Two Back-to-Back Connected MOSFETs (Q1 and Q2):
    4. 2.4 Output Slew Rate Control (R5 and C5):
    5. 2.5 Output Schottky Diode (D3) and LED Indication:
    6. 2.6 TVS Selection for 12-V Battery Protection:
    7. 2.7 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 Enable Control
    4. 5.4 Hot-Plug and Disable Using EN
    5. 5.5 Inrush Current Control
    6. 5.6 Load Response
  7. 6Board Layout and Bill of Materials
    1. 6.1 Board Layout
    2. 6.2 Bill of Materials

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 - GATE Voltage (Test Point Label GATE)
  • Channel 4 - PD Voltage (Test Point Label PD)
Set the load to 200 mA, trigger to Channel 1 rising, and turn ON the power supply. Startup behavior of LM74721EVM is captured in Figure 5-2.

GUID-20210914-SS0I-BP1J-QP8P-XTSZ1PWNHWFN-low.jpgFigure 5-2 Power Up: GATE and PD
GUID-20210914-SS0I-64M8-SJNV-KCWMHCHSQFF6-low.jpgFigure 5-3 Power Up: Charge Pump and Inrush Current

Additional startup information is captured in Figure 5-3. Channel 3 captures the internal boost converter output voltage VCAP pin during startup.