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

4.1 Relationship Between VCOMP and Se

Since the PWM comparator is a high gain element, it is reasonable to consider the positive input equal to the negative input when the high-side FET is turned off. Figure 3 shows the steady-state. Equation 4 calculates the small signal relationship between VCOMP, iL, and Se.

Fig3.gifFigure 3. PWM Comparator Input Signals
Equation 4. Eq4.gif

    where

  • iLpp is the inductor ripple current. Equation 5 calculates iLpp.
Equation 5. Eq5.gif

    where

  • Ri is the current sensing gain. Equation 1 and Equation 3 calculate Ri.
  • TON is high-side FET ON time. Equation 6 calculates TON. You can also use an oscilloscope to measure the value.
  • TOFF is high-side FET OFF time
Equation 6. Eq6.gif

    where

  • Sn is the inductor current rising slope
  • Sf is inductor current falling slope

In addition, the other parameters including the VCOMP, switching frequency (FSW), input voltage (VIN), and output voltage (VOUT) can be measured in the lab.