Equation 4

(4)

TVALLEY=π∙ LP∙CD

Since

TVALLEYcanchangealotbetweenonedesignandanother,itisnoteasytominimizetheturn-onlosses

using a fixed turn-on delay time after ZCD triggering. For this reason, the VIPERGAN50 integrates a special

function that can increase the default turn-on delay time after trigger,

TD−ONMIN

(197 ns typ.) to exactly synchronize the turn-on time at the valley of the resonance, minimizing the turn-on losses.

The pinout configuration is shown in Figure 17: the voltage divider made up by RTB and RDELAY samples the

auxiliary winding voltage which, during the GaN off-time, is representative of the output voltage.

Since in steady-state the output voltage is constant, and RTB value has already been selected to get the desired

dynamic blanking time, RDELAY can now be chosen to set the TB pin sampled voltage to the value corresponding

to the desired turn-on delay, according to Figure 20.

Figure 20. Typical Turn-on delay after triggering as function of the voltage on TB pin.

The required delay to exactly synchronize the Turn-On at the valley,

TDELAY,canbecalculatedasbelow:

Equation 5

(5)

TDELAY=TVALLEY−TZCD−DELAY

In the equation

TZCD−DELAYrepresentsthedelaybetweenthedemagnetizationtimeandtheinstantoftimein

which the ZCD voltage crosses the triggering threshold

VZCDT:thisdelayisintherangeoffewtensnsupto

hundred ns but can be easily experimentally measured during converter’s operation.

The value of

VTBcanbedirectlyreadfromthecurvealso.

Once VTB voltage is known, the value of the resistor can be easily derived:

Equation 6

(6)

RDELAY= RTB

NAUXNSEC∙VOUTVTB−1

The resistor

RTBcanbecalculatedasreportedinSection5.7Dynamicblankingtime.

The

TDELAYissettothedefaultvaluewhenRDELAYislowerthan:

Equation 7

(7)

VIPERGAN50

Valley synchronization

DS13888 - Rev 2

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