SLUAAG4 February   2022 TPS62933

 

  1.   Trademarks
  2. 1Introduction
  3. 2Loop Response of Peak Current Mode Converter
  4. 3Output Capacitance Upper Limit for Internally-Compensated PCM Buck Converter
  5. 4Output Capacitance Lower Limit for Internally-Compensated PCM Buck Converter
  6. 5Design Example and Experimental Validation for TPS62933
  7. 6Summary
  8. 7References
  9.   A Validation and Calculating the Output Capacitance Upper Limit

A Validation and Calculating the Output Capacitance Upper Limit

This appendix contains the table of validation results for the methods proposed in this document and examples using Excel or MATLAB to calculate the output capacitance upper limit.

Table A-1 Validation of Inductance Limit and Capacitance Upper Limit
VIN (V) VOUT (V) fSW (kHz) Lchoose(μH) High Limit CO(μF) Without Cff Cchoose(μF) PMbench
24 5 500 6.8 106 7 × 22 μF

(Ceffective: 92.4 μF)

 45.034
24 5 1200 3.3 119.6 8 × 22 μF

(Ceffective: 105.6 μF)

 45.827
24 12 500 12 40.7 7 × 22 μF

(Ceffective: 34.475 μF)

 46.153
Note: For VOUT = 12-V application, if CO is bigger than the high limit, add the feedforward capacitor Cff to the boost phase margin. For Cff selection, see Stability Analysis and Design of Internally-Compensated Peak Current Mode TPS62933 - Part II: How to Select the Feedforward Capacitor application note.

If Microsoft Excel is used to calculate the output capacitance upper limit, first input parameters using the following format:

  • Change the variable name of value A2-E2 to the name A1-E1.
  • Input the following equation in F2. Input “=” first, then copy and paste the expression of output capacitance upper limit for 45 degree phase margin:
    (50*(111936*IOUT - 4460544))/(441013* IOUT *VOUT*(422400/ IOUT + (8954880000/ IOUT + 178421760000/ IOUT ^2 + (2500* VIN ^2* fsw ^2)/(24649*(4356000*L + VIN - 2* VOUT)^2) - (3180000* VIN *fsw)/(157*(4356000*L + VIN - 2* VOUT)) + (84480000* VIN * fsw)/(157* IOUT *(4356000*L + VIN - 2* VOUT)) - (267632640000* VIN * fsw)/(8321* IOUT ^2*(4356000*L + VIN - 2* VOUT)) + (10560000* VIN ^2* fsw ^2)/(1306397* IOUT *(4356000*L + VIN - 2* VOUT)^2) + (11151360000* VIN ^2* fsw ^2)/(69239041* IOUT ^2*(4356000*L + VIN - 2* VOUT)^2) + 112360000)^(1/2) - (50* VIN * fsw)/(157*(4356000*L + VIN - 2* VOUT)) - (105600* VIN * fsw)/(8321* IOUT *(4356000*L + VIN - 2* VOUT)) + 10600))
  • Now the output capacitance upper limit for 45 degree phase margin can be calculated with Excel.

If MATLAB is used, implement the following code (as an example):

VIN=12;
VOUT=5;
IOUT=3;
fsw=500e3;
L=6.8e-6;
Cout_upper=(50*(111936*IOUT - 4460544))/(441013* IOUT *VOUT*(422400/ IOUT + (8954880000/ IOUT + 178421760000/ IOUT ^2 + (2500* VIN ^2* fsw ^2)/(24649*(4356000*L + VIN - 2* VOUT)^2) - (3180000* VIN *fsw)/(157*(4356000*L + VIN - 2* VOUT)) + (84480000* VIN * fsw)/(157* IOUT *(4356000*L + VIN - 2* VOUT)) - (267632640000* VIN * fsw)/(8321* IOUT ^2*(4356000*L + VIN - 2* VOUT)) + (10560000* VIN ^2* fsw ^2)/(1306397* IOUT *(4356000*L + VIN - 2* VOUT)^2) + (11151360000* VIN ^2* fsw ^2)/(69239041* IOUT ^2*(4356000*L + VIN - 2* VOUT)^2) + 112360000)^(1/2) - (50* VIN * fsw)/(157*(4356000*L + VIN - 2* VOUT)) - (105600* VIN * fsw)/(8321* IOUT *(4356000*L + VIN - 2* VOUT)) + 10600))