Datasheet A7987 (STMicroelectronics) - 10

A7987 Soft-start Figure 6. Feed-forward 5.2 Soft-start
The soft-start is essential to assure a correct and safe start-up of the step-down converter. It avoids inrush current surge and makes the output voltage increase monotonically. The soft-start is performed by charging an external capacitor, connected between SS pin and ground, with a constant current (5 µA typ.). The SS voltage is used as reference of the switching regulator and the output voltage of the converter tracks the ramp of the SS voltage. When the SS pin voltage reaches 0.8 V level, the error amplifier switches to the internal 0.8 V ±1% reference to regulate the output voltage.
DS12928
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Rev 1 page 10/37
Document Outline Cover image Product status link / summary Features Applications Description 1 Application schematic 2 Block diagram 3 Pin settings 3.1 Pin connection 3.2 Pin description 3.3 Maximum ratings 3.4 Thermal data 3.5 ESD protection 4 Electrical characteristics 5 Functional description 5.1 Oscillator and synchronization 5.2 Soft-start 5.3 Error amplifier and light-load management 5.4 Low VIN operation 5.5 Overcurrent protection 5.6 Overtemperature protection 6 Application information 6.1 Input capacitor selection 6.2 Output capacitor selection 6.3 Inductor selection 6.4 Compensation network 6.4.1 Type II compensation network 6.4.2 Type III compensation network 6.5 Thermal considerations 6.6 Layout considerations 7 Demonstration board 8 Application ideas 8.1 Positive buck-boost 8.2 Negative buck-boost 9 Package information 9.1 HTSSOP16 package information 10 Ordering information Revision history