The LM34936 has a gm error amplifier for loop compensation. The gm amplifier output (COMP) range is 0.3 V to 3 V. Connect an R_c1-C_c1 compensation network between COMP and ground for type II (PI) compensation (see Figure 8-1). Another pole is usually added using C_c2 to suppress higher frequency noise and switching frequency ripple.

The COMP output voltage (V_COMP) range limits the possible V_IN and I_OUT range for a given design. In buck mode, the maximum V_IN for which the converter can regulate the output at no load is when V_COMP reaches 0.3 V. Equation 7 gives V_COMP as a function of V_IN at no load in CCM buck mode:

Equation 7.

Where D_BUCK in the equation Equation 7 is the buck duty cycle given by:

Equation 8.

A larger L1, lower slope ripple (higher C_SLOPE), smaller sense resistor (R_SENSE), and higher frequency can increase the maximum V_IN range for buck operation.

For boost mode, the minimum V_IN for which the converter can regulate the output at full load is when V_COMP reaches 3 V. Equation 9 gives V_COMP as a function of V_IN in boost mode:

Equation 9.

Where D_BOOST in the Equation 9 is the boost duty cycle given by:

Equation 10.

A larger L1, lower slope ripple (higher C_SLOPE), smaller sense resistor (R_SENSE), and higher frequency can extend the minimum V_IN range for boost operation.