DEMO MANUAL DC242 DC/DC CONVERTER LT1777 High Voltage, Low Noise Step-Down DC/DC Converter DESCRIPTIO Demonstration Circuit DC242 is a high input voltage, low dV/dt turn-on and turn-off ramp rates. By slowing down noise step-down (buck) regulator using the LT 1777 the sharp edges during turn-on and turn-off of the power switching regulator IC. Typical applications are automo- switch, conducted and radiated EMI are significantly re- tive cellular and GPS receivers, low noise telecom and duced. The output voltage is jumper selectable to either industrial-instrument power supplies. This controller in- 3.3V or 5V. The LT1777 uses a 100kHz switching fre- cludes an onboard 700mA peak-current switch and is quency and current mode control, which offers excellent optimized for use with a high supply voltage. The input dynamic input supply rejection and short-circuit protec- voltage can range from 7.4V to 48V. In order to achieve low tion. Additionally, the supply current can be shut down to noise, the LT1777 is equipped with dI/dt limiting circuitry, less than 30m A in standby mode. Gerber files for this which is programmed via a small external inductor in the circuit are available. Call the LTC factory. power path. It also contains internal circuitry to limit the , LTC and LT are registered trademarks of Linear Technology Corporation. WWU W PERFOR A CE SU ARY T = 25 C A PARAMETER CONDITIONS VALUE Input Voltage Range I = 0mA to 500mA 7.4V to 48V OUT Output Voltage (Jumper Selectable) 3.3V, 5V Maximum Output Load Current V > 12V, V = 5V I = 500mA* IN OUT O Typical Output Ripple Voltage I = 500mA, V = 24V 17mV OUT IN P-P Nominal Operating Frequency V = 7.4V to 48V 100kHz IN I , Supply Current in Shutdown 30m A Q *I = 450mA for V 12V and V = 5V O IN OUT W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO V Switching Waveforms Component Side SW V VOLTAGE SW 10V/DIV V CURRENT SW 200mA/DIV DC242 TA01 500ns/DIV 1 UDEMO MANUAL DC242 DC/DC CONVERTER W U W SCHE ATIC A D PACKAGE DIAGRA S TP2 V IN + C4 C5 7.4V TO 48V L1 100F 0.1F TP1 200H 63V 100V L2 10 4 GND CTX200-4 0.47H V V TP3 TP6 IN CC SML32-470k 4 3 12 6 V SYNC OUT SYNC V SW 3.3V OR 5V 1 2 3 5 + TP5 C2 C1 SHDN V 500mA D 100F 1F SHDN R3 14 13 D1 U1 10V 10V 35.7k V FB TP4 C 10BQ100 LT1777 2 1 1% GND R4 NC GND C3 68k 11 8 100pF NC GND JP2 C6 C7 15 9 R2 R1 OPEN TO NC GND 100pF 680pF 26.1k 21.5k EXT SYNC 7 16 1% 1% SGND GND JP1 V OSEL OPEN = 3.3V CLOSE = 5V DC242 F01 Figure 1. 100kHz Low Noise Step-Down Switching Regulator TOP VIEW GND 1 16 GND NC 2 15 NC SHDN 3 14 V C 4 13 V FB CC V 5 12 SYNC D V 6 11 NC SW SGND 7 10 V IN GND 8 9 GND S PACKAGE 16-LEAD PLASTIC SO LT1777CS PARTS LIST REFERENCE DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE C1 1 0805ZC105MAT1A 1m F 10V 20% X7R Capacitor AVX (843) 946-0362 C2 1 TPSD107M010R0065 100m F 10V 20% Tantalum Capacitor AVX (207) 282-5111 C3, C6 2 06035A101JAT1A 100pF 50V 5% NPO Capacitor AVX (843) 946-0362 C4 1 63CV100BS 100m F 63V 20% Electrolytic Capacitor Sanyo (619) 661-6835 C5 1 12061C104MAT1A 0.1m F 100V 20% X7R Capacitor AVX (843) 946-0362 C7 1 06033A681JAT1A 680pF 25V 5% NPO Capacitor AVX (843) 946-0362 D1 1 10BQ100TR 100V 1A Schottky Diode IR (310) 322-3331 JP1, JP2 2 2802S-02G2 2mm 2-Pin Jumper Comm Con (626) 301-4200 JP1, JP2 2 CCIJ2mm-138-G 2mm 2-Pin Shunt Comm Con (626) 301-4200 L1 1 CTX200-4 200m H 0.6A SMT Inductor Coiltronics (561) 241-7876 L2 1 SML32-470K 470nH 450mA SMT Inductor Gowanda (716) 532-2234 2