L6741

Device description and operation

9/16

Bootstrap capacitor needs to be designed in order to show a negligible discharge due to the

High-Side MOSFET turn-on. In fact it must give a stable voltage supply to the High-Side

driver during the MOSFET turn-on also minimizing the power dissipated by the embedded

Boot Diode. Figure 5 gives some guidelines on how to select the capacitance value for the

bootstrap according to the desired discharge and depending on the selected mosfet.

Figure 5.

Bootstrap capacitance design

5.4

Gate driver voltage flexibility

L6741 allows the user to freely-select the gate drive voltage in order to optimize the effi-

ciency of the application.

The Low-Side MOSFET driving voltage depends on the voltage applied to VCC and can

range between 5V to 12V buses.

The High-Side MOSFET driving voltage depends on the voltage applied to PVCC (directly

impacting the bootstrap capacitor voltage) and can range between 5V to 12V buses.

5.5

Power dissipation

L6741 embeds high current drivers for both High-Side and Low-Side MOSFETs: it is then

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

to avoid overcoming the maximum junction operative temperature.

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

●

supply pins and it is simply quantifiable as follow:

●

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

dissipated to switch the MOSFETs dissipated by three main factors: external gate

resistance (when present), intrinsic MOSFET resistance and intrinsic driver resistance.

0.0

0.5

1.0

1.5

2.0

2.5

0

10

203040

5060708090

100

High-Side MOSFET Gate Charge [nC]

Cboot = 47nF

Cboot = 100nF

Cboot = 220nF

Cboot = 330nF

Cboot = 470nF

0

500

1000

1500

2000

2500

0.0

0.2

0.4

0.6

0.8

1.0

Boot Cap Delta Voltage [V]

Qg = 10nC

Qg = 25nC

Qg = 50nC

Qg = 100nC

P

DC

V

CC

I

CC

V

PVCC

I

PVCC

⋅

+

⋅

=