SLVAE22A July   2018  – March 2019 TPS54334 , TPS65251 , TPS65251-1 , TPS65251-2 , TPS65251-3 , TPS652510 , TPS65261 , TPS65263 , TPS65263-1Q1 , TPS65263-Q1 , TPS65265 , TPS65266 , TPS65266-1 , TPS65270 , TPS65273V , TPS65276V , TPS65279 , TPS65279V

 

  1.   Power Stage Gain and Slope Compensation Measurement in PCM (Peak Current Mode) BUCK Converter
    1.     Trademarks
    2. 1 Introduction
    3. 2 Unified PCM BUCK Converter
    4. 3 Power Stage Gain Measurement
      1. 3.1 Simplified Small Signal Model for Power Stage Gain
      2. 3.2 Power Stage Gain Measurement Method
    5. 4 Slope Compensation Measurement
      1. 4.1 Relationship Between VCOMP and Se
      2. 4.2 Slope Compensation Measurement Method
    6. 5 Measurement Results Verification
      1. 5.1 TPS65261 Measured GM-PS and Se
      2. 5.2 Measured Bode Plot vs. Calculated Bode Plot
    7. 6 Summary
    8. 7 References
  2.   Revision History

5.1 TPS65261 Measured GM-PS and Se

TPS65261 is a triple synchronous BUCK converter that is widely used in the market. The BUCK1 is selected to perform this verification. Set the application condition to the following:

  • 12 V VIN
  • 3.3 V VOUT
  • 3 A loading
  • 609 KHz FSW
  • 4.7 µH inductor
  • 2 × 22 µF COUT

Figure 5 shows the TPS65261 typical application circuit. R263 is changed to 10 kΩ and R262 is changed to 45.3 kΩ for the VOUT = 3.3 V setting. Due to the influence of parasitic parameters and measurement accuracy, the results shift slightly, so the average value is used for general purpose analysis.

typapp_circuit_SLVSCD3.gifFigure 5. TPS65261 Typical Application Circuit

Table 3 shows a step-by-step power stage gain (GM-PS) calculation. The average GM-PS is 7.59 A/V and it is approximately equal to 7.4 A/V provided in the TPS6526x 4.5 V to 18 V Input Voltage, 3A/2A/2A Output Current Triple Synchronous Step-Down Converter Data Sheet .

Table 3. GM-PS Calculation

STEP 1 STEP 2 STEP 3
VCOMP(V) iLoad(A) Delta VCOMP(V) Delta iLoad(A) GM-PS(A/V)
0.6075 0.50
0.6400 0.75 0.0325 0.25 7.692
0.6719 1.00 0.0319 0.25 7.837
0.7040 1.25 0.0321 0.25 7.788
0.7356 1.50 0.0316 0.25 7.911
0.7680 1.75 0.0324 0.25 7.716
0.8009 2.00 0.0329 0.25 7.599
0.8343 2.25 0.0334 0.25 7.485
0.8678 2.50 0.0335 0.25 7.463
0.9023 2.75 0.0345 0.25 7.246
0.9372 3.00 0.0349 0.25 7.163
Average Power Stage Gain GM-PS 7.590

Table 4 shows a step-by-step slope compensation (Se) calculation. The average Se is 1.86E+05 V/S.

Table 4. Se Calculation

STEP 1 STEP 2 STEP 3 STEP 4
VIN(V) VCOMP(V) Calculated TON(uS) Calculated iLpp(A) Delta VCOMP(V) Delta VIN(V) Delta iLpp(A) Calculated Se(V/S)
4.5 0.9727 1.204 0.307
5 0.9409 1.084 0.392 -0.0318 0.5 0.042 2.18E+05
5.5 0.9165 0.985 0.461 -0.0244 0.5 0.035 2.01E+05
6 0.8972 0.903 0.519 -0.0193 0.5 0.029 1.89E+05
6.5 0.8812 0.834 0.568 -0.0160 0.5 0.024 1.84E+05
7 0.8668 0.774 0.609 -0.0144 0.5 0.021 1.96E+05
7.5 0.8541 0.722 0.646 -0.0127 0.5 0.018 2.00E+05
8 0.8432 0.677 0.677 -0.0109 0.5 0.016 1.95E+05
8.5 0.8340 0.637 0.705 -0.0092 0.5 0.014 1.85E+05
9 0.8259 0.602 0.730 -0.0081 0.5 0.012 1.82E+05
9.5 0.8187 0.570 0.752 -0.0072 0.5 0.011 1.81E+05
10 0.8119 0.542 0.772 -0.0068 0.5 0.010 1.92E+05
10.5 0.8061 0.516 0.791 -0.0058 0.5 0.009 1.79E+05
11 0.8009 0.493 0.807 -0.0052 0.5 0.008 1.75E+05
11.5 0.7961 0.471 0.822 -0.0048 0.5 0.008 1.78E+05
12 0.7918 0.452 0.836 -0.0043 0.5 0.007 1.73E+05
12.5 0.7878 0.433 0.849 -0.0040 0.5 0.006 1.75E+05
13 0.7842 0.417 0.860 -0.0036 0.5 0.006 1.70E+05
13.5 0.7807 0.401 0.871 -0.0035 0.5 0.005 1.80E+05
14 0.7774 0.387 0.881 -0.0033 0.5 0.005 1.84E+05
Average Slope Compensation Se 1.86E+05