L6731B

Device description

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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 3. Pins function):

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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 about 100ns. The valley-current-protection is enabled when the low-side

MOSFET(s) is turned on after a masking time of about 400ns. 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.

the OCH comparator triggers an over current the high-side MOSFET(s) is immediately turned

off (after the masking time and the internal delay) and returned on at the next pwm cycle. The

because during the masking time the peak-current-protection is disabled. In case of very hard

is very helpful in this case to limit the current. If during the off-time the OCL comparator triggers

an over current, the high-side MOSFET(s) is not turned on until the current is over the valley-

current-limit. This implies that, if it is necessary, some pulses of the high-side MOSFET(s) will

be skipped, guaranteeing a maximum current due to the following formula:

In constant current protection a current control loop limits the value of the error amplifier output

(comp), in order to avoid its saturation and thus recover faster when the output returns in

regulation. Figure 9. shows the behaviour of the device during an over current condition that

persists also in the soft-start phase.

Figure 8.

OVP: the low-side MOSFET is turned-on in advance.

LGate

109%

MIN

ON

VALLEY

MAX

T

L

Vout

Vin

I

I

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