L6743D

Device description and operation

11/16

Referring to Figure 6, classical MOSFET driver can be represented by a push-pull output

stage with two different MOSFETs: P-MOSFET to drive the external gate high and N-

MOSFET to reach the driving voltage (PVCC for HS and VCC for LS). This capacitance is

The total power Psw is dissipated among the resistive components distributed along the

driving path. According to the external Gate resistance and the power-MOSFET intrinsic

gate resistance, the driver dissipates only a portion of Psw as follow:

The total power dissipated from the driver can then be determined as follow:

Figure 6.

Equivalent circuit for MOSFET drive

4.5

Layout guidelines

L6743D provides driving capability to implement high-current step-down DC-DC converters.

The first priority when placing components for these applications has to be reserved to the

power section, minimizing the length of each connection and loop as much as possible. To

minimize noise and voltage spikes (also EMI and losses) power connections must be a part

of a power plane and anyway realized by wide and thick copper traces: loop must be anyway

minimized. The critical components, such as the power MOSFETs, must be close one to the

other. However, some space between the power MOSFET is still required to assure good

thermal cooling and airflow.

Traces between the driver and the MOSFETS should be short and wide to minimize the

inductance of the trace so minimizing ringing in the driving signals. Moreover, VIAs count

needs to be minimized to reduce the related parasitic effect.

P

SW

HS

–

1

2

--- C

GHS

PVCC

2

Fsw

R

hiHS

R

hiHS

R

GateHS

R

iHS

++

----------------------------------------------------------------

R

loHS

R

loHS

R

GateHS

R

iHS

++

----------------------------------------------------------------

+

⎝⎠

⎛⎞

⋅⋅

⋅

⋅

=

P

SW

LS

–

1

2

--- C

GLS

VCC

2

Fsw

R

hiLS

R

hiLS

R

GateLS

R

iLS

++

--------------------------------------------------------------

R

loLS

R

loLS

R

GateLS

R

iLS

++

--------------------------------------------------------------

+

⎝⎠

⎛⎞

⋅⋅

⋅

⋅

=

PP

DC

P

SW

HS

–

P

SW

LS

–

++

=

VCC

LS DRIVER

LS MOSFET

GND

LGATE

BOOT

HS DRIVER

HS MOSFET

PHASE

HGATE

VCC