Datasheet L6981 (STMicroelectronics) - 9
| Manufacturer | STMicroelectronics |
| Description | 38 V, 1.5 A synchronous step-down converter with low quiescent current |
| Pages / Page | 49 / 9 — L6981. Soft-start. 6.2. Figure 5. Soft-start procedure. DS13554. Rev 1. … |
| File Format / Size | PDF / 3.5 Mb |
| Document Language | English |
L6981. Soft-start. 6.2. Figure 5. Soft-start procedure. DS13554. Rev 1. page 9/49
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L6981 Soft-start
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: 1. Thermal shutdown event 2. UVLO event 3. EN pin rising over VEN threshold. Please refer to Table 6.
DS13554
-
Rev 1 page 9/49
Document Outline 1 Diagram 2 Pin configuration 3 Typical application circuit 4 Absolute maximum ratings 5 Electrical characteristics 6 Functional description 6.1 Enable 6.2 Soft-start 6.3 Undervoltage lockout 6.4 Light-load operation 6.4.1 Low consumption mode (LCM) 6.4.2 Low noise mode (LNM) 6.4.3 Efficiency for Low consumption mode and Low noise mode part number 6.4.4 Load regulation for low consumption mode and low noise mode part number 6.5 Overvoltage protection 6.5.1 Low consumption mode part number 6.5.2 Low noise mode part number 6.6 Overcurrent protection 6.7 Thermal shutdown 7 Closing the loop 7.1 GCO(s) control to output transfer function 7.2 Error amplifier compensation network 7.3 Voltage divider 8 Design of the power components 8.1 Programmable power up threshold 8.2 External synchronization (only available for Low Noise Mode) 8.3 Output voltage adjustment 8.4 Design of the power components 8.4.1 Input capacitor selection 8.4.2 Inductor selection 8.4.3 Output capacitor selection 9 Application board 10 Efficiency curves 11 Thermal dissipation 12 Package information 12.1 SO 8L package information 13 Ordering information Revision history
L6981 Soft-start
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: 1. Thermal shutdown event 2. UVLO event 3. EN pin rising over VEN threshold. Please refer to Table 6.
DS13554
-
Rev 1 page 9/49
Document Outline 1 Diagram 2 Pin configuration 3 Typical application circuit 4 Absolute maximum ratings 5 Electrical characteristics 6 Functional description 6.1 Enable 6.2 Soft-start 6.3 Undervoltage lockout 6.4 Light-load operation 6.4.1 Low consumption mode (LCM) 6.4.2 Low noise mode (LNM) 6.4.3 Efficiency for Low consumption mode and Low noise mode part number 6.4.4 Load regulation for low consumption mode and low noise mode part number 6.5 Overvoltage protection 6.5.1 Low consumption mode part number 6.5.2 Low noise mode part number 6.6 Overcurrent protection 6.7 Thermal shutdown 7 Closing the loop 7.1 GCO(s) control to output transfer function 7.2 Error amplifier compensation network 7.3 Voltage divider 8 Design of the power components 8.1 Programmable power up threshold 8.2 External synchronization (only available for Low Noise Mode) 8.3 Output voltage adjustment 8.4 Design of the power components 8.4.1 Input capacitor selection 8.4.2 Inductor selection 8.4.3 Output capacitor selection 9 Application board 10 Efficiency curves 11 Thermal dissipation 12 Package information 12.1 SO 8L package information 13 Ordering information Revision history
