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

2.2.1 SW Output Voltage Setpoint

The output voltage of the switcher is set by the resistor divider network of R5 and R6. R6 is fixed at 10 kΩ. To change the switcher output voltage of the EVM, it is necessary to change the value of resistor R5. The value of R5 for a specific output voltage can be calculated using Equation 1. Note that the SW output must be 0.8 V above the LDO output for best PSR and noise performance.

Equation 1. R5 = 10 kΩ (SW VOUT – 0.8 V) / (0.8 V)

Table 2-1 lists the R5 values for some common output voltages. The values given in Table 2-1 are standard values, not the exact value calculated using Equation 1.

Table 2-1 Sample 1% Resistor Values for Common SW Output Voltages
SW OUTPUT VOLTAGE (V)R5 VALUE (kΩ)
1.812.4
2.521.5
3.331.6
4.141.2
552.3
664.9