5 Driver section

L6722

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5

Driver section

The integrated high-current drivers allow using different types of power MOS (also multiple

MOS to reduce the equivalent RdsON), maintaining fast switching transition.

The drivers for the high-side mosfets use BOOTx pins for supply and PHASEx pins for return.

The drivers for the low-side mosfets use the VCC pin for supply and PGND pin for return.

The controller embodies a anti-shoot-through and adaptive dead-time control to minimize low

side body diode conduction time maintaining good efficiency saving the use of Schottky diodes:

when the high-side mosfet turns off, the voltage on its source begins to fall; when the voltage

reaches 2V, the low-side mosfet gate drive is suddenly applied. When the low-side mosfet turns

off, the voltage at LGATEx pin is sensed. When it drops below 1V, the high-side mosfet gate

drive is suddenly applied. If the current flowing in the inductor is negative, the source of high-

side mosfet will never drop. To allow the low-side mosfet to turn-on even in this case, a

watchdog controller is enabled: if the source of the high-side mosfet doesn't drop, the low side

mosfet is switched on so allowing the negative current of the inductor to recirculate. This

mechanism allows the system to regulate even if the current is negative.

Power conversion input is flexible: 5V, 12V bus or any bus that allows the conversion (See

Section 7.3) can be chosen freely.

5.1

Power dissipation

L6722 embeds high current mosfet 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. 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 in the device power dissipation: bias power and drivers' power.

●

pins and it is simply quantifiable as follow (assuming to supply HS and LS drivers with the

same VCC of the device):

Figure 5.

Dissipated power

P

DC

V

CC

I

CC

3I

BOOTx

⋅

+

(

)

⋅

=

L6722; Rgate=0; Rmosfet=0

0

500

1000

1500

2000

2500

3000

3500

4000

50

100

150

200

250

300

350

400

450

500

550

Switching frequency [kHz] per phase

HS=1xSTS12NH3LL; LS=1xSTS25NH3LL

HS=1xSTS12NH3LL; LS=2xSTS25NH3LL

HS=1xSTD55NH2LL; LS=1xSTD95NH02L

HS=2xSTD55NH2LL; LS=2xSTD95NH02L

L6722; Rhs=2.2; Rls=3.3; Rmosfet=1

0

500

1000

1500

2000

2500

3000

3500

4000

50

100

150

200

250

300

350

400

450

500

550

Switching Frequency per phase [kHz]

HS=1xSTS12NH3LL; LS=1xSTS25NH3LL

HS=1xSTS12NH3LL; LS=2xSTS25NH3LL

HS=1xSTD55NH22L; LS=1xSTD95NH02L

HS=2xSTD55NH22L; LS=2xSTD95NH02L