DC378 INTRODUCTION Description Demonstration circuit DC378 is a synchronous step-down buck regulator using the LTC1778 No RSENSE switching regulator controller. The controller uses a valley current control architecture to deliver very low duty cycles without requiring a sense resistor. It provides high efficiency operation at light loads by means of discontinuous mode operation. Noise and RF interference are reduced by a forced continuous control pin. With a wide operating range of VIN = 4V to 36V and duty cycles of 2% to 90% at 200kHz, the LTC1778 is ideal for the applications such as notebook and palmtop computers, PDAs, battery chargers and distributed power systems. + – + – + – JP2 SD RUN/SS PGND ON VIN 5V–25V GND + VOUT 2.5V/10A JP1 DISC CONT – + – LOAD GND LTC1778CGN GND No Rsense™ Wide Operating Range DC/DC/Converter EXTVCC Figure 1. DC378A Test and Measurement Setup Quick Start Guide This demonstration board is easily set up to evaluate the performance of the LTC1778. Please consult Figure 1 and follow the procedure outlined below for proper operation. 1. Connect input power to the VIN and GND terminals. Input voltage is limited to between 5V to 28V. 2. Connect the load between the VOUT and GND terminals. 3. Set the FCB Jumper JP1 to the lower position (CONT) to force continuous synchronous operation at low loads, or to the upper position (DISC) to enable discontinuous mode operation at low loads. 4. To shut down the circuit, connect the RUN/SS pin to ground by setting jumper JP2 to the SD position. Set JP2 to the ON position to enable normal operation. 5. When measuring input or output ripple, see Figure 2 for proper scope probe technique. GND Vout Figure 2. Scope Probe Placement for Measuring Output Ripple 5 4 3 2 1 D D 5 6 7 8 4 1 C 2 3 BOOST 16 PGOOD TG 15 VRNG SW 14 PGND 13 BG 12 RUN/SS 4 FCB 5 ITH 6 SGND INTVcc 11 7 ION VIN 10 8 VFB EXTVcc 1 2 3 C 5 6 7 8 4 1 2 3 9 B B A A 5 4 3 2 1 Bill Of Material Demo Bd. #378A Linear Technology Corporation LTC1778CGN 6/16/2005 3:52 PM Item Qty Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 1 1 1 1 3 0 2 1 1 0 1 1 1 1 1 8 2 1 1 1 1 1 1 1 1 1 1 1 1 1 2 4 4 1 2 1 CB1 CC1 CC2 CF CIN1,CIN2,CIN3 CON (Optional) COUT1,COUT2 CSS CVCC C1,C2,C3 (Optional) C4 C5 C6 DB D1 E1-E8 JP1,JP2 L2 M1 M2 RF1 RON RPG1 RSS1 R1 R2 R3 R4 R5 U1 XJP2,XJP1 Part Description Capacitor, X7R 0.22uF 16V 10% Capacitor, X7R 560pF 25V 10% Capacitor, NPO 100pF 50V 10% Capacitor, Y5V 0.1uF 25V 80% Capacitor, X5R 10uF 25V 20% Capacitor, X7R 0.01uF 25V 10% Capacitor, Spcl. Poly. 180uF 4V 20% Capacitor, X7R 0.1uF 16V 10% Capacitor, X5R 4.7uF 6.3V 20% Capacitor, X7R TBD 50V 10% Capacitor, X7R 0.01uF 25V 10% Capacitor, X5R 22uF 6.3V 20% Capacitor, Alum 10uF 35V 10% Schottky Diode, Super-Mini Schottky Rect., 40V/3Amp Turret Headers, 3 Pins 2mm Ctrs. Inductor, 1uH, D104C Mosfet., N-Chan. Red. Qg Mosfet., N-Chan. Red. Qg Resistor, Chip 1 OHM 0.06W 5% Resistor, Chip 715K 0.06W 1% Resistor, Chip 100K 0.06W 5% Resistor, Chip 510K 0.06W 5% Resistor, Chip 14K 0.06W 1% Resistor, Chip 30.1K 0.06W 1% Resistor, Chip 11K 0.06W 5% Resistor, Chip 39K 0.06W 5% Resistor, Chip 20K 0.06W 5% I.C., NO Rsense Stepdown Controller SHUNT, CCIJ2MM-138-G STAND-OFF, NYLON HEX #4-40 1/4" SCREW, #4-40, 1/4" PRINTED CIRCUIT BOARDS STENCIL SOLDER FRAME Page 1 - of - 1 Manufacture / Part # AVX 0805YC224KAT1A AVX 06033C561MAT2A AVX 06035A101KAT1A AVX 06033G104ZAT2T Taiyo Yuden TMK432BJ106MM AVX 06033C103KAT2A PANASONIC EEFUE0G181R AVX 0603YC104KAT1A Taiyo Yuden JMK212BJ475MD-T AVX 06035C101KAT1A AVX 06033C103KAT2A Taiyo Yuden JMK325BJ226MM-T SANYO 35CV10gX Central Semi. Corp CMDSH-3 B340A Diodes Inc. Mill Max 2501-2 CommConn Con Inc. 2802S-03G2 Toko 919AS-1R0N Siliconix Si4884DY Siliconix Si4874DY AAC CR16-1R0JM AAC CR16-7153FM AAC CR16-104JM AAC CR16-514JM AAC CR16-1402FM AAC CR16-3012FM AAC CR16-113JM AAC CR16-393JM AAC CR16-203JM Linear Technology Corp. LTC1778CGN COMM CON. CCIJ2MM-138-G MICRO PLASTICS 14HTSP101 ANY DEMO BOARD DC378A STENCIL DC378A FRAME S/N# 10695