L6732TR datasheet(16/36 Pages) STMICROELECTRONICS

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Device description

L6732

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5.7

Driver section

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

MOSFETs to reduce the RDSON), 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 20ns. 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 (-350mV 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 rises with a slope

of 100mV/µs, emulating in this way the breaking of the high-side MOSFET as an over-voltage

cause.

Figure 10. OVP

LGate

L6732TR Datasheet(PDF) 16 Page - STMicroelectronics