The LNM device regulates the output voltage with valley sinking capability down to the negative current limitation

(IVY_SINK in Figure OVP Event Low Noise Mode part number). This hysteretic operating mode between peak

current mode threshold (ISKIP_LNM) and modulated low side switch conduction time for VOUT regulation

persists until the valley current level triggers the negative current limitation (IVY_SINK), that is the maximum

sinking capability of the device (highlighted in green in figure above).

If the source injection further increases, the output voltage is a partitioning between source impedance and

maximum sinking capability above described (highlighted in blue in figure above).

6.6

Over current protection

The current protection circuitry features a constant current protection, so the device limits the maximum peak

current (please refer to Table 6) in an overcurrent condition.

The L6982 device implements a pulse-by-pulse current sensing on both power elements (high-side and low-side

switches) for effective current protection over the duty cycle range. The high-side current sensing is called “peak”,

the low-side sensing “valley”.

The internal noise generated during the switching activity makes the current sensing circuitry ineffective for a

minimum conduction time of the power element. This time is called “masking time” because the information from

the analog circuitry is masked by the logic to prevent an erroneous detection of the overcurrent event. Therefore,

the peak current protection is disabled for a masking time after the high-side switch is turned on. The masking

time for the valley sensing is activated after the low-side switch is turned on. In other words, the peak current

protection can be ineffective at extremely low duty cycles, the valley current protection at extremely high duty

cycles.

The L6982 device assures an effective overcurrent protection sensing the current flowing in both power elements.

In case one of the two current sensing circuitries is ineffective because of the masking time, the device is

protected, sensing the current on the opposite switch. Thus, the combination of the “peak” and “valley” current

limits assure the effectiveness of the overcurrent protection even in extreme duty cycle conditions.

L6982

Over current protection

DS13683 - Rev 1

page 18/48