L7981 3 A step-down switching regulator Datasheet - production data Industrial: PLD, PLA, FPGA, chargers Networking: XDSL, modems, DC-DC modules Computer: VFQFPN8 3 x 3 HSOP8 exposed pad Optical storage, hard disk drive, printers, audio/graphic cards Suitable for LED driving Features 3 A DC output current Description 4.5 V to 28 V input voltage The L7981 device is a step-down switching Output voltage adjustable from 0.6 V regulator with a 3.7 A (minimum) current limited 250 kHz switching frequency, programmable embedded Power MOSFET, so it is able to deliver up to 1 MHz up to 3 A current to the load depending on the application conditions. Internal soft-start and enable Low dropout operation: 100% duty cycle The input voltage can range from 4.5 V to 28 V, while the output voltage can be set starting from Voltage feed-forward 0.6 V to V . IN Zero load current operation Requiring a minimum set of external components, Overcurrent and thermal protection the device includes an internal 250 kHz switching VFQFPN 3 x 3 - 8L and HSOP8 package frequency oscillator that can be externally adjusted up to 1 MHz. Applications The QFN and the HSOP packages with exposed pad allow reducing the R down to 60C/W and thJA Consumer: 40C/W respectively. STB, DVD, DVD recorder, car audio, LCD TV and monitors Figure 1. Application circuit May 2014 DocID15182 Rev 5 1/42 This is information on a product in full production. www.st.comContents L7981 Contents 1 Pin settings 4 1.1 Pin connection 4 1.2 Pin description 4 2 Maximum ratings 5 3 Thermal data . 5 4 Electrical characteristics . 6 5 Functional description . 8 5.1 Oscillator and synchronization 9 5.2 Soft-start .11 5.3 Error amplifier and compensation 12 5.4 Overcurrent protection . 13 5.5 Enable function 14 5.6 Hysteretic thermal shutdown 14 6 Application informations 15 6.1 Input capacitor selection 15 6.2 Inductor selection . 16 6.3 Output capacitor selection 17 6.4 Compensation network . 18 6.4.1 Type III compensation network . 20 6.4.2 Type II compensation network 24 6.5 Thermal considerations 27 6.6 Layout considerations . 28 6.7 Application circuit . 30 7 Application ideas . 34 7.1 Positive buck-boost . 34 7.2 Inverting buck-boost . 36 2/42 DocID15182 Rev 5