SLUUCK3 November   2021 TPS563212

 

  1. 1Introduction
  2. 2Performance Specification Summary
  3. 3Modifications
    1. 3.1 MODE Pin Configuration
    2. 3.2 Output Voltage Setpoint
  4. 4Test Setup
    1. 4.1 Input/Output Connections
    2. 4.2 Start-Up Procedure
  5. 5Board Layout
    1. 5.1 Layout
    2. 5.2 EVM Picture
  6. 6Schematic, List of Materials, and Reference
    1. 6.1 Schematic
    2. 6.2 List of Materials
  7. 7Reference

3.2 Output Voltage Setpoint

The output voltage is set with a resistor divider from the output node to the FB pin. TI recommends using 1% tolerance or better divider resistors. Referring to the application schematic of Figure 6-1, start with 10 kΩ or 20 kΩ for R9 and use Equation 1 to calculate R8. To improve efficiency at light loads, consider using larger value resistors. If the values are too high, the regulator is more susceptible to noise and voltage errors from the FB input current are noticeable.

Equation 1. GUID-480830B9-5DDA-468A-B680-FB4761641E06-low.gif

Table 3-2 lists the R8 and R9 values for some common output voltages. Note that the values given in Table 3-2 are standard values and not the exact value calculated using above equation.

Table 3-2 Recommended Component Values
OUTPUT VOLTAGE(1) (V) R8(2) (kΩ) R9 (kΩ) L1(3) (µH) COUT(4) (µF) RANGE of L1·COUT_E(5) (μH × μF) C7(6) (pF)
0.76 5.36 20.0 0.56 2 × 22 17 to 130 —
1.05 15.0 20.0 0.68 2 × 22 17 to 130 10 to 100
1.8 40.0 20.0 1.0 1 × 22 15 to 160 10 to 100
2.5 31.6 10.0 1.5 1 × 22 15 to 160 10 to 100
3.3 45.3 10.0 2.2 1 × 22 15 to 160 10 to 100
5 73.2 10.0 3.3 1 × 22 15 to 160 10 to 100
(1) Use the recommended L1 and COUT combination of the higher and closest output rail for the unlisted output rails.
(2) R8 = 10 kΩ and R9 = Float for VOUT = 0.6 V
(3) Inductance values are calculated based on VIN=18 V, but they can also be used for other input voltages. Users can calculate their preferred inductance value per the TPS563212 4.2-V-18-V Input, 3-A Synchronous Buck Converter in a SOT-5X3 Package Data Sheet.
(4) The COUT is the sum of nominal output capacitance. 22-μF, 0805, 10-V or higher specification capacitors are recommended .
(5) The COUT_E is the effective value after derating. The value of L1·COUT_E should be within in the range.
(6) R6 and C7 can be used to improve the load transient response and improve the loop-phase margin.