SLVU641A January   2012  – November 2021 TPS54120

 

  1.   Trademarks
  2. 1Background
  3. 2Setup
    1. 2.1 Input and Output Connections and Jumper Descriptions
    2. 2.2 Modifications
      1. 2.2.1 SW Output Voltage Setpoint
      2. 2.2.2 LDO Output Voltage Setpoint
      3. 2.2.3 Switcher Slow-Start Time
      4. 2.2.4 LDO Start-Up
    3. 2.3 Equipment Interconnect
  4. 3Operation
  5. 4Test Results
    1. 4.1 Output Voltage Ripple
    2. 4.2 Output Noise
    3. 4.3 Output Turn-On
    4. 4.4 Load Transient
    5. 4.5 Efficiency
    6. 4.6 Thermal Characteristic
  6. 5Board Layout
    1. 5.1 Layout Description
  7. 6Schematic
  8. 7Bill of Materials
  9. 8Revision History

2.2.3 Switcher Slow-Start Time

The slow-start time can be adjusted by changing the value of C7. Use Equation 3 to calculate the required value of C7 for a desired slow-start time (TSS).

Equation 3. C7(nF) = TSS(ms) ISS(μA) / VREF(V)

Basically, the device has an internal pullup current source of ISS = 2.3 μA that charges the external slow-start capacitor, C7. The voltage reference VREF (V) for this part is 0.8 V.