The TPS61033 uses a valley current limit sensing scheme. Current limit detection occurs during the off-time by sensing of the voltage drop across the synchronous rectifier.

When the load current is increased such that the inductor current is above the current limit within the whole switching cycle time, the off-time is increased to allow the inductor current to decrease to this threshold before the next on-time begins (so called frequency foldback mechanism). When the current limit is reached, the output voltage decreases during further load increase.

The maximum continuous output current (I_OUT(LC)), before entering current limit (CL) operation, can be defined by Equation 2.

Equation 2.

where

• D is the duty cycle
• ΔI_L(P-P) is the inductor ripple current

The duty cycle can be estimated by Equation 3.

Equation 3.

where

• V_OUT is the output voltage of the boost converter
• V_IN is the input voltage of the boost converter
• η is the efficiency of the converter, use 90% for most applications

The peak-to-peak inductor ripple current is calculated by Equation 4.

Equation 4.

where

• L is the inductance value of the inductor
• f_SW is the switching frequency
• D is the duty cycle
• V_IN is the input voltage of the boost converter