ZHCSTC5A October 2023 – March 2024 LM51772
ADVANCE INFORMATION
For stable current loop operation and to avoid subharmonic oscillations, the slope resistor must be selected based on Equation 24:
The next higher value has to be selected which is 0.825 and then be set via RCFG1 or the I2C interface. This slope compensation results in “dead-beat” operation, in which the current loop disturbances die out in one switching cycle. Theoretically, a current mode loop is stable with half the “dead-beat” slope (considered already in the calculated slope resistor value in Equation 24). A smaller slope capacitor results in larger slope signal, which is better for noise immunity in the transition region (VIN is approximately equal to VOUT). A larger slope signal, however, restricts the achievable input voltage range for a given output voltage, switching frequency, and inductor. For this design, a slope compensation factor of 0.875 (see Configuration Pin CFG2) is selected for better transition region behavior while still providing the required VIN range. This selection of slope capacitor, inductor, switching frequency, and inductor satisfies the COMP range limitation.