L6728D

Application details

Doc ID 16498 Rev 1

19/33

Figure 7.

Power connections (heavy lines)

Gate traces and phase traces must be sized according to the driver RMS current delivered

to the power MOSFET. The device robustness allows the management of applications with

the power section far from the controller without compromising performance. In any case,

when possible it is recommended to minimize the distance between the controller and

power section.

Small signal components and connections to critical nodes of the application, as well as

bypass capacitors for the device supply, are also important. Locate bypass capacitor (VCC

and bootstrap capacitor) and feedback compensation components as close to the device as

leakage current paths on the LGATE / OC pin, since internal current source is only 10 µA.

Systems that do not use a Schottky diode in parallel to the low-side MOSFET might show

big negative spikes on the phase pin. This spike must be limited within the absolute

maximum ratings (for example, adding a gate resistor in series to the HS MOSFET gate), as

well as the positive spike, but has an additional consequence: it causes the bootstrap

capacitor to be over-charged. This extra charge can cause, in the worst-case condition of

maximum input voltage and during particular transients, that boot-to-phase voltage

overcomes the absolute maximum ratings, also causing device failures. It is then suggested

in this cases to limit this extra charge by adding a small resistor in series to the bootstrap

diode.

Figure 8.

Driver turn-on and turn-off paths

L

UGATE

PHASE

LGATE

GND

LOAD

L6728A

L6728D

VCC

LS DRIVER

LS MOSFET

GND

LGATE

BOOT

HS DRIVER

HS MOSFET

PHASE

UGATE