L6718 datasheet(66/71 Pages) STMICROELECTRONICS

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Power dissipation and application details

L6718

66/71

DocID023399 Rev 3

Equation 17

•

Driver power is the power needed by the driver to continuously switch ON and OFF the

external MOSFETs; it is a function of the switching frequency and total gate charge of

the selected MOSFETs. It can be quantified considering that the total power PSW

dissipated to switch the MOSFETs is dissipated by three main factors: external gate

resistance (when present), intrinsic MOSFET resistance and intrinsic driver resistance.

This last term is the important one to be determined in order to calculate the device

power dissipation.

The total power dissipated to switch the MOSFETs for each phase featuring an

embedded driver results:

Equation 18

where QGHSx is the total gate charge of the HS MOSFETs and QGLSx is the total gate

charge of the LS MOSFETs for both CORE and NB sections (only Phase1 and Phase2

for CORE section); VBOOTx is the driving voltage for the HSx MOSFETs.

External gate resistors help the device to dissipate the switching power as the same

power (PSW) is shared between the internal driver impedance and the external resistor

resulting in a general cooling of the device. When diving multiple MOSFETs in parallel,

it is suggested to use one resistor on each MOSFET.

VCCDR

⋅

SWx

GHSx

VCCDR

⋅

GLSx

VBOOTx

⋅

()

⋅

L6718 Datasheet(PDF) 66 Page - STMicroelectronics