The device can control the inductor current in three different ways to regulate the output:
During PWM-CCM operation, the device switches at a constant frequency and the inductor current is continuous (see Figure 9-2). PWM operation achieves the lowest output voltage ripple and the best transient performance.
During PWM-DCM operation, the device switches at a constant frequency and the inductor current is discontinuous (see Figure 9-3). In this mode, the device controls the peak inductor current to maintain the selected switching frequency while still being able to regulate the output.
During PFM-DCM operation, the device keeps the peak inductor current constant (at a level corresponding to the minimum on time of the converter) and skips pulses to regulate the output (see Figure 9-4). The switching pulses that occur during PFM-DCM operation are synchronized to the internal clock.
Use Equation 1 to calculate the output current threshold at which the device enters PFM-DCM.
Figure 9-5 shows how this threshold typically varies with VIN and VOUT for a switching frequency of 2.25 MHz.
Table 9-1 shows the function table of the MODE/SYNC pin and the FPWMEN bit in the CONTROL1 register, which control the operating mode of the device.
|MODE/SYNC Pin||FPWMEN Bit||Operating Mode||Remark|
|Low||0||PSM||Do not use in a stacked configuration.|