The VG(θ) voltage is then managed by the “THD-DCM optimizer” circuitry that acts as a simple gain (K2) in CCM

operation whereas in DCM operation opportunely shapes the VG(θ) voltage in order to achieve ideally sinusoidal

input current.

Considering the CCM operation, the VCS_REF(θ) voltage is then expressed by:

Equation 2

(2)

VCS_REFθCCM=VGθ  K2= KMVOUT VC  VINθ

where

KM=K1 K2istheequivalentmultipliergain(seeElectricalcharacteristicstablefordetails).

The internal current reference voltage VCS_REF(θ) is then compared with the current sense VCS(θ) pin voltage

(which is internally translated due to negative inductor current sensing) that is opportunely shaped by the “THD-

CCM optimizer” in order to achieve sinusoidal input current in CCM operation.

In particular, referring to Section 5.1 Figure 4 and Section 5.1 Figure 5, during the power switch-on time

the “THD-CCM optimizer“ circuitry sources a current ITHD_CCM(θ) to the CS pin, generating a voltage across the

external RTHD_CCM resistor that is subtracted to the inductor current sense voltage

 RS  ILθ.

The resulting VCS(θ) voltage, at external power switch turn-off condition, is then:

Equation 3

(3)

VCSθ = RS  IL,PKθ −  RTHD_CCM  ITHDCCMθ =VCS_REFθ

where the sourced ITHD_CCM(θ) current is:

Equation 4

E

(4)

ITHD_CCMθ = LP2 KCCM ΔILθ

LP is the inductor value, ∆IL(θ) is the inductor current ripple, KCCM (0.55 typ.) is the circuitry gain.

Figure 5. Left key waveforms of the circuit in figure

4

Figure 6. Right key waveforms of the circuit in

figure 4

L4985

Theory of operation

DS13769 - Rev 3

page 11/27