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

2 Unified PCM BUCK Converter

Figure 1 shows a PCM Buck converter, which is usually composed of several key blocks. It includes the following:

  • Error Amplifier (EA)
  • PWM Comparator (PWM)
  • Slope Compensation (SLP)
  • Current Sensing (CS)
  • Clock (CLK)
  • Power Stage
  • Output Stage

The RC network after error amplifier compensates for the output pole and increases loop gain for stability. Typically, Figure 1 can explain PCM BUCK converters.

Fig1.gifFigure 1. PCM BUCK Converter Block Diagram

During normal operation, the voltage difference between the internal reference voltage (Vref) and the feedback voltage (VFB) is amplified and outputs at COMP node. The clock signal (CLK) turns on high-side FET. The sensed current (CS) compares with the COMP voltage minus slope compensation (SLP) and the output logic is set to turn off high-side FET. The low-side FET turns on for the rest of the period.

Assuming the operating frequency is fixed, the slope compensation is linear, and the COMP is a pin that you can use to measure its voltage at this node. The whole application is explained based on this unified PCM model in CCM (Continuous Current Mode).