L6706 datasheet(42/47 Pages) STMICROELECTRONICS

42 / 47 page

Power dissipation

L6706

42/47

Doc ID 15698 Rev 2

Power dissipation

L6706 embeds high current MOSFET drivers for both high side and low side MOSFETs: 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.

Exposed pad needs to be soldered to the PCB power ground plane through several VIAs in

order to facilitate the heat dissipation.

Two main terms contribute in 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 it is simply quantifiable as follow (assuming to supply HS and LS drivers with the same

VCC of the device):

Drivers' 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 (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 MOSFETs results:

External gate resistors helps 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 MOSFETs in parallel, it is

suggested to use one gate resistor for each MOSFET.

Figure 25.

L6706 dissipated power (quiescent + switching)

CCDR

BOOT

()

⋅

GHS

BOOT

⋅

GLS

CCDR

⋅

()

⋅

L6706 Datasheet(PDF) 42 Page - STMicroelectronics