L6714 datasheet(30/70 Pages) STMICROELECTRONICS

30 / 70 page

Power dissipation

L6714

30/70

Power dissipation

L6714 embeds high current MOSFET drivers for both high side and low side MOSFET: it is

then important to consider the power the device is going to dissipate in driving them in order

to avoid overcoming the maximum junction operative temperature. In addition, since the

device has an exposed pad to better dissipate the power, the thermal resistance between

junction and ambient consequent to the layout is also important: thermal pad need to be

soldered to the PCB ground plane through several VIAs in order to facilitate the heat

dissipation.

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

The first one (PDC) depends on the static consumption of the device through the supply pins

and is simply quantifiable as follows (assuming to supply HS and LS drivers with the same

VCC of the device):

where N is the number of phases.

Drivers' power is the power needed by the driver to continuously switch on and off the

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

selected MOSFET. It can be quantified considering that the total power PSW dissipated to

switch the MOSFET (easy calculable) 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 MOSFET results:

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

power PSW will be shared between the internal driver impedance and the external resistor

resulting in a general cooling of the device. When driving multiple MOSFET in parallel, it is

suggested to use one gate resistor for each MOSFET.

CCDRx

⋅

BOOTx

⋅

()

⋅

GHS

BOOT

⋅

GLS

CCDRx

⋅

()

⋅⋅

L6714 데이터시트(PDF) 30 Page - STMicroelectronics