4.2 Slope Compensation Measurement Method

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

Equation 7.

Figure 4. V_se for A Different Duty

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

Equation 8 and Equation 9 calculate the different V_se1 and V_se2.

Equation 8.

Equation 9.

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

Equation 10.

where

• F_SW and R_i stay constant relative to V_IN

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

1. Measure V_COMP at different V_IN values in the CCM from low V_IN to high V_IN.
2. Use Equation 5 to calculate T_ON for each condition. Use Equation 4 to calculate i_Lppfor each condition.
3. Subtract V_COMP, V_IN, and i_Lpp with the next data.
4. Use Equation 10 to calculate S_e for each condition.

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