L6981 datasheet(9/49 Pages) STMICROELECTRONICS

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When the voltage applied on the EN pin rises over VWAKEUP, RISING, the device powers up the internal circuit

increasing the current consumption.

As soon as the voltage rises over the VEN, RISING, the device starts the switching activities as described in

Section 6.2 Soft-start.

Once the voltage becomes lower than VEN,FALLING, the device interrupts the switching activities.

As soon as the voltage becomes lower than VWAKEUP,FALLING, the device powers down the internal circuit

reducing the current consumption.

The pin is VIN compatible.

Please refer to Table 6 for the reported thresholds.

6.2

Soft-start

The soft-start (SS) limits the inrush current surge and makes the output voltage increase monotonically.

The device implements the soft-start phase ramping the internal reference with very small steps. Once the SS

ends, the Error Amplifier reference is switched to the internal value of 0.85 V coming directly from the band gap

cell.

Figure 5. Soft-start procedure

During normal operation, a new soft-start cycle takes place in case of:

Thermal shutdown event

UVLO event

EN pin rising over VEN threshold. Please refer to Table 6.

L6981

Soft-start

DS13554 - Rev 1

page 9/49

L6981 Datasheet(PDF) 9 Page - STMicroelectronics