Driver section

L6726A

10/24

5

Driver section

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

The driver for high-side MOSFET uses BOOT pin for supply and PHASE pin for return. The

driver for low-side MOSFET uses the VCC pin for supply and GND pin for return.

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

low side body diode conduction time, maintaining good efficiency while saving the use of

Schottky diode:

●

to check for high-side MOSFET turn off, PHASE pin is sensed. When the voltage at

PHASE pin drops down, the low-side MOSFET gate drive is suddenly applied;

●

to check for low-side MOSFET turn off, LGATE pin is sensed. When the voltage at

LGATE has fallen, the high-side MOSFET gate drive is suddenly applied.

If the current flowing in the inductor is negative, voltage on PHASE pin 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

maximum duty cycle limitation and recommended operating conditions) can be chosen

freely.

5.1

Power dissipation

L6726A 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.

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

●

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

drivers with the same VCC of the device):

●

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, the voltage supply of the

driver and total gate charge of the selected MOSFETs. It can be quantified considering

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 MOSFETs results:

P

DC

V

CC

I

CC

I

BOOT

+

()

⋅

=

P

SW

F

SW

Q

gHS

V

BOOT

V

PHASE

–

() Q

gLS

V

CC

⋅

+

⋅

[]

⋅

=