Device description

L6725 - L6725A

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5.7

Driver section

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

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. 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 8).

The device realizes the over-current-protection (OCP) sensing the current both on the high-side

MOSFET(s) and the low-side MOSFET(s) and so 2 current limit thresholds can be set (see

OCH pin and OCL pin in Table 4: Pin functions):

●

Peak Current Limit

●

Valley Current Limit

The Peak Current Protection is active when the high-side MOSFET(s) is turned on, after a

masking time of 100ns. The valley-current-protection is enabled when the low-side MOSFET(s)

is turned on after a masking time of 500ns. If, when the soft-start phase is completed, an over

current event occurs during the on time (peak-current-protection) or during the off time (valley-

current-protection) the device enters in HICCUP mode: the high-side and low-side MOSFET(s)

are turned off, the soft-start capacitor is discharged with a constant current

of 10µA and when

the voltage at the SS pin reaches 0.5V the soft-start phase restarts (see Figure 9).

Figure 8.

OVP

LGate

FB