L6714 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6714
STMicroelectronics
'L6714' PDF : 70 Pages View PDF
Power dissipation
9
Power dissipation
L6714
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):
PDC = VCC ⋅ (ICC + N ⋅ ICCDRx + N ⋅ IBOOTx)
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:
PSW = N ⋅ FSW ⋅ (QGHS ⋅ VBOOT + QGLS ⋅ VCCDRx)
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.
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