DC270A Analog Devices

DEMO MANUAL DC270 NO-DESIGN SWITCHER LTC1772 Constant Frequency Current Mode Step-Down DC/DC Converter U DESCRIPTIO Demo board DC270 is a step-down (buck) regulator using attractive for noise-sensitive applications. In addition, the LTC1772. The exclusive use of surface mount compo- high efficiency over a wide load current range makes the LTC1772 ideal for battery-powered applications. In drop- nents results in a highly efficient application in a very small board space. It is ideal for cell phones and other portable out, the external P-channel MOSFET is turned on continu- electronics operating from one or two Li-Ion cells or three ously (100% duty cycle), providing low dropout operation to six NiCd cells. DC270 is capable of providing 1A at an with V V . To further enhance efficiency at low load OUT IN TM output voltage of 2.5V with an input supply of 4.2V. This currents, the LTC1772 is configured for Burst Mode demo board highlights the capabilities of the LTC1772, operation. The LTC1772 is capable of operating down to which uses a current mode PWM architecture to drive an approximately 2.2V input voltage before the undervoltage external P-channel power MOSFET. The result is a high lockout feature is activated. Gerber files for this circuit performance power supply that has low output voltage board are available. Call the LTC factory. ripple. Constant operating frequency makes the LTC1772 , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. WWU W PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS VALUE V Input Working Voltage Range V = 2.5V 2.5V to 9.8V IN OUT V Output Voltage I = 1A 2.5V 0.0625V OUT OUT V Feedback Voltage 0.8V 0.02V FB I Typical Supply Current Normal Mode V = 4.2V, I = 0mA 220m A Q IN OUT Shutdown V = 4.2V, V = 0V 7m A IN ITH/RUN W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO Efficiency vs Load Current Component Side 100 V = 3.3V IN 90 V = 5V IN 80 V = 8V IN 70 60 50 V = 2.5V OUT R = 0.03 SENSE 40 1 10 100 1000 10000 LOAD CURRENT (mA) DC270 TA01 1 EFFICIENCY (%)DEMO MANUAL DC270 NO-DESIGN SWITCHER WWU W PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS VALUE I Maximum Output Current V = 4.2V, V = 2.5V 1A (Min) OUT IN OUT D V Typical Load Regulation 0mA I 1A, V = 8.5V 1% OUT OUT IN V Typical Output Ripple in Burst Mode Operation I = 100mA, V = 4.2V 120mV RIPPLE OUT IN P-P PACKAGE A D SCHE ATIC DIAGRA SM + SHDN V IN C C C1 IN U1 R 220pF C1 10F LTC1772 10k R 10V 1 6 CS I /RUN PGATE TH 0.040 GND 2 5 GND V IN 3 4 TOP VIEW V SENSE FB R F2 4 5 6 I /RUN 1 6 PGATE TH 80.6k R F1 1% 174k GND 2 5 V IN M1 1% V 3 4 SENSE FDC638P FB L1 S6 PACKAGE 4.7H 3 2 1 6-LEAD PLASTIC SOT-23 V OUT 2.5V C O2 LTC1772CS6 D1 + C O1 4.7F MBRM120T3 47F 6.3V 6V OPTIONAL GND DC270 F01 Figure 1. LTC1772 Constant Frequency, Current Mode, Step-Down DC/DC Converter Schematic PARTS LIST REFERENCE DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE C 1 6TPA47M 47m F 6V POSCAP Capacitor Sanyo (619) 661-6835 O1 C (Optional) 1 JMK212BJ475MG 4.7m F 6.3V Capacitor Taiyo Yuden (408) 573-4150 O2 C 1 LMK325BJ106K-T 10m F 10V Capacitor Taiyo Yuden (408) 573-4150 IN C 1 06035A221KAT 220pF 10% NPO Capacitor AVX (843) 946-0362 C1 D1 1 MBRM120T3 Schottky Diode ON Semiconductor (602) 244-6600 L1 1 DO1608C-472 4.7m H Inductor Coilcraft (847) 639-6400 M1 1 FDC638P MOSFET Fairchild (408) 822-2126 R 1 LR1206-01-R040F 0.040W 1% 0.25W 1206 Resistor IRC (361) 992-7900 CS R 1 CR16-103JM 10k 5% 1/8W 0603 Resistor TAD (800) 508-1521 C1 R 1 CR16-1743FM 174k 1% 0.1W 0603 Resistor TAD (800) 508-1521 F1 R 1 CR16-8062FM 80.6k 1% 0.1W 0603 Resistor TAD (800) 508-1521 F2 U1 1 LTC1772CS6 6-Pin SOT-23 IC LTC (408) 432-1900 2 W WU