Driver section

A6727

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5

Driver section

The integrated high-current drivers allow different types of power MOSFET to be used (also

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

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

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

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

Schottky diode:

•

the device senses the PHASE pin to check that high-side MOSFET is off. When the

sensed voltage drops below an internal threshold, the low-side MOSFET is suddenly

turned on.

•

the device senses the LGATE pin to check that low-side MOSFET is off. When the

sensed voltage drops below an internal threshold, the high-side MOSFET is suddenly

turned on.

If the current flowing in the inductor is negative, the voltage on PHASE pin never drops. 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: 5 V, 12 V bus or any bus that allows the conversion (see

maximum duty cycle limitation and recommended operating conditions, in Table 5) to be

chosen freely.

5.1

Power dissipation

The A6727 embeds high-current MOSFET drivers for both high-side and low-side

MOSFETs. The dissipated power by the device avoids overcoming the maximum junction

operative temperature.

Two main terms contribute to the device power dissipation: bias power and driver power.

•

pins and it is calculated as follows (assuming to supply HS and LS drivers with the

same VCC of the device):

Equation 1

•

Driver 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 of

dissipated by three main factors: external gate resistance (when present), intrinsic

MOSFET resistance and intrinsic driver resistance. This last term has to be determined

to calculate the device power dissipation. The total power dissipated to switch the

MOSFETs is:

P

DC

V

CC

I

CC

I

BOOT

+

()

⋅

=