L6739 datasheet(18/30 Pages) STMICROELECTRONICS

18 / 30 page

High current embedded drivers

L6739

18/30

DocID026384 Rev 1

8.2

Power dissipation

It is important to consider the power that the device is going to dissipate in driving the

external MOSFETs in order to avoid surpassing the maximum junction operative

temperature.

Two main terms contribute in the device power dissipation: bias power and drivers' power.



Device power (PDC) depends on the static consumption of the device through the

supply pins and it is simply quantifiable as follows:

Equation 8



Driver's 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 to calculate the device power

dissipation.

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

driver results:

Equation 9

where QGHS is the total gate charge of the HS MOSFETs and QGLS is the total gate

charge of the LS MOSFETs.

PDC

VCC ICC VVCCDR IVCCDR



PSW

FSW QGHS VCCDR



QGLS VCCDR







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