L6728AH datasheet(17/33 Pages) STMICROELECTRONICS

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L6728AH

Application details

Doc ID 15726 Rev 1

17/33

Figure 7.

Power connections (heavy lines)

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

the power MOSFET. The device robustness allows managing applications with the power

section far from the controller without losing performances. Anyway, when possible, it is

recommended to minimize the distance between 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

practical. For over current programmability, place ROCSET close to the device and avoid

leakage current paths on COMP/OC pin, since the internal current source is only 60

μA.

Systems that do not use 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 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 boot capacitor (one resistor in series

to BOOT).

Figure 8.

Drivers turn-on and turn-off paths

CIN

VIN

UGATE

PHASE

LGATE

GND

LOAD

L6728A

COUT

L6728AH

RGATE

RINT

CGD

CGS

CDS

VCC

LS DRIVER

LS MOSFET

GND

LGATE

RGATE

RINT

CGD

CGS

CDS

BOOT

HS DRIVER

HS MOSFET

PHASE

UGATE

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