8.5.1.1

Deadtime

Deadtime between LS on and HS on is set by connecting a resistor between DT pin and ground, according to the

following formula:

tDT_LS_HS=3.88ns+1.46nskΩ∙RDT

(6)

Deadtime between HS and LS is instead controlled by the controller parameter DT_HVG_LVG according to the

formula:

tDT_HS_LS=DT_HVG_LVG

FCK

(7)

Where FCK is the IC clock frequency of 132 MHz.

8.5.1.2

Synchronous rectification voltage

The synchronous rectifier turn-on voltage is clamped to a programmable value. The user can choose the driving

voltage which yields the best application performance.

The driver is powered from the VDRV pin.

8.5.2

Skip mode

In order to improve the efficiency at medium load, the controller enters in valley skipping mode when the peak

current falls below a programmable value.

While in skip mode the controller keeps the peak current approximately constant at the skipping mode entry point.

If the frequency falls below approximately 20 kHz, the controller starts dropping the peak current while keeping

the frequency limited between 20 kHz and a programmable value (typ. 50 kHz).

Figure 9. Transition between normal mode, skip mode and burst mode

Iload

fsw

Ipk

Normal mode

Valley skipping

20kHz

ipkMinSkip

Burst

8.5.3

Burst mode

While in skip mode, if the frequency drops below FCK/6500 (approximately 20 kHz) the system enters burst mode.

While in burst mode the controller generates bursts of pulses with a programmable peak current. The number of

pulses generated depends on the output voltage and can be programmed through the parameters.

The system exits burst mode and comes back to normal operation when the average time between bursts drops

below a programmable time.

8.5.3.1

Deep burst

When the regulated output voltage is 5 V, 9 V, 15 V or 20 V, all the IC functions are shut down between the bursts,

leaving only a dedicated comparator to wake up the system when a new burst is required. In this condition, the

consumption of the secondary side IC drops to Isleep. For any other regulation voltage, the burst is controlled by

the firmware and ADC readings, so the IC consumption between bursts is close to the normal mode operating

current.

ST-ONEMP

Switching modes

DS13989 - Rev 2

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