L6732_08 datasheet(16/37 Pages) STMICROELECTRONICS

16 / 37 page

Device description

L6732

16/37

5.7

Driver section

The high-side and low-side drivers allow using different types of power MOSFETs (also

multiple MOSFETs to reduce the RDS(on) maintaining fast switching transitions.

The low-side driver is supplied by VCCDR while the high-side driver is supplied by the BOOT

pin. A predictive dead time control avoids MOSFETs cross-conduction maintaining very

short dead time duration in the range of 20 ns. The control monitors the phase node in order

to sense the low-side body diode recirculation. If the phase node voltage is less than a

certain threshold (-350 mV typ.) during the dead time, it will be reduced in the next PWM

cycle. The predictive dead time control doesn't work when the high-side body diode is

conducting because the phase node doesn't go negative. This situation happens when the

converter is sinking current for example and, in this case, an adaptive dead time control

operates.

5.8

Monitoring and protections

The output voltage is monitored by means of pin FB. If it is not within ±10 % (typ.) of the

programmed value, the Power good (PGOOD) output is forced low.

The device provides over-voltage-protection: when the voltage sensed on FB pin reaches a

value 20% (typ.) greater than the reference, the low-side driver is turned on as long as the

over voltage is detected (see Figure 10.).

It must be taken into account that there is an electrical network between the output terminal

and the FB pin and therefore the voltage at the pin is not a perfect replica of the output

voltage. However due to the fact that the converter can sink current, in the most of cases the

low-side will turn-on before the output voltage exceeds the over-voltage threshold, because

the error amplifier will throw off balance in advance. Even if the device doesn't report an

over-voltage, the behavior is the same, because the low-side is turned-on immediately. The

following figure shows the device behavior during an over-voltage event. The output voltage

Figure 10.

OVP

LGate

L6732 Datasheet(PDF) 16 Page - STMicroelectronics