L6981 datasheet(19/49 Pages) STMICROELECTRONICS

Part #	L6981

Description	38 V, 1.5 A synchronous step-down converter with low quiescent current

PDF	49 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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In case the current diverges because of the high-side masking time, the low-side power element is turned on until

the switch current level drops below the valley current sense threshold. The low-side operation is able to prevent

the high-side turn-on, so the device can skip pulses decreasing the switching frequency.

Figure 20. Overcurrent protection behavior

In a worst case scenario, reported in Figure 20 of the overcurrent protection, the switch current is limited to:

IMAX=IVY+VIN−VOUT

L ∙TMASKHS

(4)

Where IVY is the current threshold of the valley sensing circuitry (please refer to Electrical characteristics table)

and TMASKHS is the masking time of the high-side switch.

In most of the overcurrent conditions, the conduction time of the high-side switch is higher than the masking time

and so the peak current protection limits the switch current.

IMAX=IPEAKTH

(5)

The DC current flowing in the load in overcurrent condition is:

IDCOUT=IMAX−IRIPPLEVOUT

2 =IMAX− VIN− VOUT

2∙L ∙TON

(6)

L6981

Overcurrent protection

DS13554 - Rev 1

page 19/49

L6981 Datasheet(PDF) 19 Page - STMicroelectronics