If the MODE pin is HIGH, the converter maintains a forced-PWM operation for all load currents.

t1/f

SWt

Time

0

T

ON

Figure 8-1. Continuous Conduction Mode (PWM-CCM) Current Waveform

8.3.2 Power Save Mode (PSM) Operation

To maintain high efficiency at light loads, the device enters power save mode (PSM) at the boundary to

discontinuous conduction mode (DCM). This event happens when the output current becomes smaller than

half of the ripple current of the inductor. The device operates with a fixed on-time, and the switching frequency

decreases proportional to the load current as shown in Figure 8-2. It can be calculated as:

fPSM= 2×IOUT

TON2× VINVOUTVIN−VOUTL

(2)

Time

0

Skipped Pulses

t1/fPSMt

Figure 8-2. Discontinuous Conduction Mode (PSM-DCM) Current Waveform

In PSM, the output voltage rises slightly above the nominal target, which can be minimized using larger output

capacitance. At duty cycles larger than 90%, the device does not enter PSM and maintains output regulation in

PWM mode.

8.3.3 Start-Up and Soft Start

When the EN voltage goes High, the device starts loading the default values into the device registers. This

action typically is done within 120 μs. After that, the internal soft-start circuitry controls the output voltage during

start-up. This control avoids excessive inrush current and makes sure of a controlled output voltage ramp. This

control also prevents unwanted voltage drops from high-impedance power sources or batteries. Finally, the PG

signal has a delay up to 180 μs at start-up. Figure 8-3 shows a start-up sequence, where the EN pin is pulled up

to VIN.

TPS628301, TPS628302, TPS628303, TPS628304

SLVSG98A – FEBRUARY 2023 – REVISED OCTOBER 2023

www.ti.com

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