The TLV61047 operates at a quasi-constant frequency pulse width modulation (PWM) under heavy to light load conditions. As the load current decreases, the output of the internal error amplifier also decreases to lower the inductor peak current and delivers less power. The PWM mode can be divided into CCM-PWM mode and DCM-PWM mode based on the load conditions.

• The device operates in CCM-PWM mode with a heavy to moderate load. During this phase, the inductor current valley is always above zero.

• The device operates in DCM-PWM mode as the load continues to decrease from moderate to light. As the name DCM (Discontinuous Current Mode) suggests, an obvious characteristic of this mode is that the inductor current remains at zero for one period in each cycle. During this phase, the inductor peak current can still be reduced by the output of the internal error amplifier to maintain the balance between input and output power. This allows a suitable off-time of the low-side FET to be worked out internally to keep the switching frequency quasi-constant without pulse skipping. This phase ends when the inductor peak current decreases to I_{CALMP_LOW}, which is typically 20mA.

After the peak inductor current reaches the I_{CLAMP_LOW} and the load decreases to ultra-light or even no load, the peak inductor current can't be smaller. To balance the input and output energy, the low-side FET is turned off for a prolonged period. The duration of the "zero inductor current" is much longer than in the DCM-PWM phase. This phase is called DCM-PFM mode for features of discontinuous inductor current and significantly reduced frequency. The three phases of CCM-PWM, DCM-PWM and DCM-PFM are shown in the Figure 7-1.

In work conditions where the V_IN is very close to the V_OUT, the V_IN V_OUT ratio decided turn on time may be less than the minimum turn on time, the device also enters into the DCM-PFM mode.

At light load, when T_ON min is triggered the device also enters DCM-PFM mode even if the inductor peak current is greater than I_{CALMP_LOW}. When the low-side FET is turned on, it remains on for a minimum time, called T_ON min. The inductor is energised for at least T_ON min time when the low-side FET is on. If the T_ON min is greater than the ideal time required to maintain the quasi-constant frequency, the device has to extend the off time to balance the input and output energy. So the device is in DCM-PFM mode. Under normal work conditions, the T_ON min triggered DCM-PFM mode is much more common than that triggered by I_{CALMP_LOW}, unless an inductor with extremely large inductance is used.