Figure 4-13 shows the efficiency at 4mA and 20mA load current. Observe that the efficiency range TPS629203 is from 80.3% to 82.1%, which is a high efficiency while meeting the requirements of external capacitance.

Figure 4-13 Efficiency with a 5.6uH Inductor

If the ripple limit can be relaxed, then the efficiency can be further improved. In a cycle time T_cycle, the charge of inductor ΔQ_L is equal to charge consumed by load in Figure 4-13. So, T_cycle can be calculated by using Equation 10.

For buck converters with constant on time, T_cycle can be increased by reducing the inductor L, which means less switching loss and higher efficiency. However, this leads to increased ripple in Equation 3 and Equation 8.

Figure 4-14 Cycle Time in DCM

Figure 4-15 shows a comparison of the efficiency of the inductor of 2.2uH (ripple is 0.5% of input and output voltage) and 5.6uH inductor (ripple is 0.2% of input and output voltage). Observe that the efficiency has increased to 86.8%-87.7%.

Figure 4-15 Efficiency with 2.2uH Inductor and 5.6uH Inductor