7.4.2 Pulse Skip Eco-Mode

The TPS57060-Q1 device operates in a pulse-skip Eco mode at light load currents to improve efficiency by reducing switching and gate drive losses. The TPS57060-Q1 device is designed so that if the output voltage is within regulation and the peak switch current at the end of any switching cycle is below the pulse skipping current threshold, the device enters Eco mode. This current threshold is the current level corresponding to a nominal COMP voltage of 500 mV.

When in Eco-mode, the COMP pin voltage is clamped at 500 mV and the high-side MOSFET is inhibited. Further decreases in load current or in output voltage cannot drive the COMP pin below this clamp voltage level.

Because the device is not switching, the output voltage begins to decay. As the voltage control loop compensates for the falling output voltage, the COMP pin voltage begins to rise. At this time, the high-side MOSFET is enabled and a switching pulse initiates on the next switching cycle. The peak current is set by the COMP pin voltage. The output voltage re-charges the regulated value (see Figure 50), then the peak switch current starts to decrease, and eventually falls below the Eco mode threshold at which time the device again enters Eco mode.

For Eco mode operation, the TPS57060-Q1 device senses peak current, not average or load current, so the load current where the device enters Eco mode is dependent on the minimum on-time, input voltage, output voltage, and output inductance value. For example, the circuit in Figure 51 enters Eco mode at about 20 mA of output current. When the load current is low and the output voltage is within regulation, the device enters a sleep mode and draws only 116-μA input quiescent current. The internal PLL remains operating when in sleep mode. When operating at light load currents in the pulse skip mode, the switching transitions occur synchronously with the external clock signal.

Figure 50. Pulse-Skip Mode Operation