EVAL5981 1 A step-down switching regulator demonstration board based on the L5981 Data Brief Features 1 A DC output current 2.9 V to 18 V input voltage Output voltage adjustable from 0.6 V to 16 V 250 kHz switching frequency, programmable up to 1 MHz Internal soft-start and inhibit Low dropout operation: 100 % duty cycle Zero-load current operation Over-current and thermal protection VFQFPN8 3 mm x 3 mm package EVAL5981 Description The compensation network on the demonstration The EVAL5981 demonstration board provides the board allows the use of MLCC as output filter to design engineer with a fully functional step-down keep the loop stable. The inductor saturation switching regulator with an output current of up to current and forward current of the Schottky diode 1 A. The L5981 integrates STMicroelectronics are within the current limit values. step-down switching regulator, together with all the external components required for a typical The switching frequency on the demonstration application. board is set to 500 kHz by means of the R5 resistor connected to pin Fsw. The rated voltage of the input capacitor and the Schottky diode rectifier repetitive peak reverse voltage are both 25 V, making the board capable of covering the entire 2.9 V - 18 V input voltage range of the L5981 device. The board features an external resistor divider (R1 and R2) designed for an output voltage of 3.3 V. The output voltage can be set to a level from 0.6 V up to the rated voltage of the output capacitor (16 V). March 2009 Rev 1 1/6 For further information contact your local STMicroelectronics sales office. www.st.com 6EVAL5981 EVAL5981 application circuit and component list 1 EVAL5981 application circuit and component list Figure 1. Application circuit L1L1 15 15uuHH VINVINVINVIN====3.3.3.3.3V t3V t3V t3V toooo 18 18 18 18VVVV VCCVCCVCCVCC OUOUOUOUTTTT Vout=3Vout=3Vout=3Vout=3.3V.3V.3V.3V 11111111 8888 D1D1D1D1 SYNCSYNCSYNCSYNCHHHH ININININHHHH 3333 2222 STSTSTSTPSPSPSPS2L25U2L25U2L25U2L25U C2C2C2C2 L5L5L5L5985981981985 GNDGNDGNDGND 7777 FBFBFBFB R1R1R1R1 4 4 4 4....99999999KKKK 22222222uuuuFFFF C1C1C1C1 C6C6C6C6 5555 6666 4444 10101010uuuuFFFF 68686868nnnnFFFF C4C4C4C4 1 1 1 10000nFnFnFnF FSFSFSFSWWWW COMPCOMPCOMPCOMPCOMPCOMPCOMPCOMP R3R3 1 18800 C3C3 3 3..3nF3nF R4R4 3. 3.9K9K R5R5 10 100K0K RRRR2222 1. 1. 1. 1.1K1K1K1K CC55 15 150pF0pF Table 1. Component list Reference Part number Description Manufacturer C1 GRM31CR61E106KA12 10 F, 25 V MURATA C2 GRM32ER61E226KE15 22 F, 25 V MURATA C3 3.3 nF, 50 V C4 10 nF, 50 V C5 150 pF, 50 V C6 68 nF, 25 V R1 4.99 k , 1 %, 0.1 W 0603 R2 1.1 k , 1 %, 0.1 W 0603 R3 180 , 1 %, 0.1 W 0603 R4 3.9 k , 1 %, 0.1 W 0603 R5 100 k , 1 %, 0.1 W 0603 D1 STPS2L25V 2 A, 25 V STMicroelectronics L1 7447779115 15 H, 20 %, 2.2 A Wurth elektronik 2/6