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

4.2 Slope Compensation Measurement Method

Slope compensation (Se) or Vse cannot be measured directly. It cannot be measured like GM-PS at a different loading since Vse does not change with the loading, but changes with duty. Equation 7 calculates Vse in a steady-state for a different duty under the same loading, but different VIN condition. Figure 4 illustrates Vse.

Equation 7. Eq7.gif
Fig4.gifFigure 4. Vse for A Different Duty

Since directly measured VCOMP contains DC bias voltage, which introduces error, the Se must be calculated by a differentiated method.

Equation 8 and Equation 9 calculate the different Vse1 and Vse2.

Equation 8. Eq8.gif
Equation 9. Eq9.gif

Equation 10 calculates Se. Subtract Equation 9 from Equation 8 and reform it.

Equation 10. Eq10.gif

    where

  • FSW and Ri stay constant relative to VIN

Table 2 shows step-by-step Se calculation guidelines.

  1. Measure VCOMP at different VIN values in the CCM from low VIN to high VIN.
  2. Use Equation 5 to calculate TON for each condition. Use Equation 4 to calculate iLppfor each condition.
  3. Subtract VCOMP, VIN, and iLpp with the next data.
  4. Use Equation 10 to calculate Se for each condition.

For some parts, the FSW and Ri are not constant. More accuracy Se values can be obtained by measuring FSW for each condition and measuring current sensing gain Ri. Section 3 describes this process.

Table 2. Se Calculation Guidelines

STEP 1 STEP 2 STEP 3 STEP 4
VCOMP VIN TON iLpp Delta VCOMP Delta VIN Delta iLpp Se
VCOMP1 VIN1 TON1 iLpp1
VCOMP2 VIN2 TON2 iLpp2 VCOMP2 - VCOMP1 VIN2 - VIN1 iLpp2 - iLpp1 Equation 10
VCOMP3 VIN3 TON3 iLpp3 VCOMP3 - VCOMP2 VIN3 - VIN2 iLpp3 - iLpp2 Equation 10
... ... ... ... ... ... ... ...
VCOMP(N) VIN(N) TON(N) iLpp(N) VCOMP(N) - VCOMP(N-1) VIN(N) - VIN(N-1) iLpp(N) - iLpp(N-1) Equation 10