AN4402 datasheet(22/39 Pages) STMICROELECTRONICS

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Demagnetization energy

AN4402

22/39

DocID025557 Rev 1

Moreover the factor

increases rapidly as VBAT gets closer to the clamping voltage. The impact of this term is

sometimes overlooked, although it is responsible for a drastic increase of the clamp energy

at high VBAT.

Assuming that the inductance is constant, independently from the current level IL0 (no

saturation of the inductance), the demagnetization energy increases faster than a square

function of VBAT, especially when the battery voltage is close to the clamping voltage.

Figure 12. Contribution of the factor 1 / (1 - (VCL_LS/VBAT)) to the increase EDEMAG with

VBAT

The gate-source clamp is activated

From Equation 24, we observe that the dissipated energy in a high-side configured output,

when the gate-source clamp is activated exceeds the energy stored in the inductor. It is also

due to the additional energy which is supplied by the battery during the turn-off phase.

Equation 24:

Moreover, the demagnetization energy in this case increases faster than a square function

of VBAT due to the additional term:

CL_LS

BAT

–

----------------------------------------

CL_LS

BAT

-------------------

–

-----------------------------

DEMAG1_HS

∞

→

lim

--- LI

CL_HS

BAT

CL_HS

----------------------------------------







BA T

CL_HS

-------------------

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