TPS62933O datasheet(14/47 Pages) TI

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8.3 Feature Description

8.3.1 Fixed Frequency Peak Current Mode

The following operation description of the TPS62933 refers to the functional block diagram and to the waveforms

in Figure 8-1. The TPS62933 is a synchronous buck converter with integrated high-side (HS) and low-side (LS)

MOSFETs (synchronous rectifier). The TPS62933 supplies a regulated output voltage by turning on the HS

and LS NMOS switches with controlled duty cycle. During high-side switch on time, the SW pin voltage swings

up to approximately VIN, and the inductor current, iL, increases with linear slope (VIN – VOUT) / L. When the

HS switch is turned off by the control logic, the LS switch is turned on after an anti-shoot–through dead time.

Inductor current discharges through the low-side switch with a slope of –VOUT / L. The control parameter of a

buck converter is defined as Duty Cycle D = tON / TSW, where tON is the high-side switch on time and TSW is

the switching period. The converter control loop maintains a constant output voltage by adjusting the duty cycle

D. In an ideal buck converter where losses are ignored, D is proportional to the output voltage and inversely

proportional to the input voltage: D = VOUT / VIN.

VSW

VIN

D = tON/ TSW

tON

tOFF

TSW

IOUT

ILPK

¨LL

Figure 8-1. SW Node and Inductor Current Waveforms in Continuous Conduction Mode (CCM)

The TPS62933 employs the fixed-frequency peak current mode control. A voltage feedback loop is used to

get accurate DC voltage regulation by adjusting the peak current command based on voltage offset. The

peak inductor current is sensed from the HS switch and compared to the peak current threshold to control

the on time of the HS switch. The voltage feedback loop is internally compensated, which allows for fewer

external components, makes it easy to design, and provides stable operation with almost any combination of

output capacitors. The converter operates with fixed switching frequency at normal load condition. At light-load

condition, the TPS62933 operates in PFM mode to maintain high efficiency.

8.3.2 Pulse Frequency Modulation

The TPS62933 is designed to operate in pulse frequency modulation (PFM) mode at light load currents to boost

light load efficiency.

When the load current is lower than half of the peak-to-peak inductor current in CCM, the TPS62933 operates

in discontinuous conduction mode (DCM). In DCM operation, the low-side switch is turned off when the inductor

current drops to approximately 0 A to improve efficiency. Both switching losses and conduction losses are

reduced in DCM, compared to forced CCM operation at light load.

At even lighter current load, pulse frequency modulation (PFM) mode is activated to maintain high-efficiency

operation. When either the minimum high-side switch on time tON_MIN or the minimum peak inductor current

IPEAK_MIN (typically 750 mA) is reached, the switching frequency decreases to maintain regulation. In PFM mode,

TPS62933

SLUSEA4A – JUNE 2021 – REVISED DECEMBER 2021

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