8.2.1.2 Detailed Design Procedure

The first step in the design procedure is to verify that the maximum possible output current of the boost converter supports the specific application requirements. A simple approach is to estimate the converter efficiency by taking the efficiency numbers from the provided efficiency curves or to use a worst case assumption for the expected efficiency (for example: 90%).

Duty cycle (D) is calculated with Equation 1.

Equation 1.

Maximum output current (I_out(max)) is calculated with Equation 2.

Equation 2.

Peak switch current in application (I_swpeak) is calculated with Equation 3.

Equation 3.

The inductor peak-to-peak ripple current (ΔI_L) is calculated with Equation 4.

Equation 4.

where

• V_IN is the minimum input voltage.
• V_S is the output voltage.
• I_LIM(min) is the converter switch current limit (minimum switch current limit = 3.2 A).
• f_S is the converter switching frequency (typically 1.2 MHz or 650 kHz).
• L is the selected inductor value.
• η is the estimated converter efficiency (use the number from the efficiency plots or 90% as an estimation).

The peak switch current is the steady state peak switch current that the integrated switch, inductor, and external Schottky diode must be able to handle. The calculation must be done for the minimum input voltage where the peak switch current is the highest.