L6747A

Device description and operation

Doc ID 17126 Rev 1

11/15

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

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

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

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

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

Figure 6.

Equivalent circuit for a MOSFET driver

4.5

Layout guidelines

The L6747A provides driving capability to implement high-current step-down DC-DC

converters.

The first priority when placing components for these applications should be given to the

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

minimize noise and voltage spikes (as well as EMI and losses) power connections must be

part of a power plane, and in any case constructed with wide and thick copper traces. The

loop must be minimized. The critical components, such as the power MOSFETs, must be

close to each other. However, some space between the power MOSFETs is required to

assure good thermal cooling and airflow.

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