DEMO MANUAL DC232 NO-DESIGN SWITCHER LTC1622 Low Input Voltage Current Mode Step-Down U DC/DC Converter DESCRIPTIO Demo board DC232 is a step-down (buck) regulator using out, the external P-channel MOSFET is turned on continu- the LTC1622. The exclusive use of surface mount compo- ously (100% duty cycle), providing low dropout operation nents results in a highly efficient application in a very small with V V . To further enhance efficiency at low load OUT IN TM board space. It is ideal for cell phones and other portable currents, the LTC1622 can be set up for Burst Mode electronics operating from one or two Li-Ion cells or three operation or pulse skipping mode by either connecting the to six NiCd cells. DC232 is capable of providing 1.5A at an SYNC/MODE pin to V or leaving it disconnected. The IN output voltage of 2.5V with an input supply of 4.2V. This LTC1622 can also be synchronized to an external clock at demo board highlights the capabilities of the LTC1622, frequencies of up to 750kHz. The LTC1622 is capable of which uses a current mode PWM architecture to drive an operating down to a 2V input voltage before the undervoltage lockout feature is activated. Soft start is external P-channel power MOSFET. The results are a high performance power supply that has low output voltage provided by an external capacitor, which can also be used ripple. Constant operating frequency makes the LTC1622 to properly sequence supplies. Gerber files for this circuit attractive for noise-sensitive applications. In addition, board are available. Call the LTC factory. high efficiency over wide load current range makes the , LTC and LT are registered trademarks of Linear Technology Corporation. LTC1622 ideal for battery-powered applications. In drop- 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 = 1.8V 2V to 8.5V IN OUT V Output Voltage I = 800mA 3.3V 0.033V OUT OUT I = 800mA 2.5V 0.025V OUT I = 800mA 1.8V 0.018V OUT V Feedback Voltage 0.8V 0.04V FB I Typical Supply Current Normal Mode V = 4.2V, I = 0mA 400A Q IN OUT Shutdown V = 4.2V, V = 0V 15A IN RUN/SS W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO Efficiency vs Load Current Efficiency vs Load Current (Burst Mode Enabled) (Burst Mode Defeated) Board Photo 100 100 V = 3.3V IN V = 3.3V IN V = 4.2V IN 90 90 V = 4.2V IN 80 80 V = 8.4V IN 70 V = 6V 70 IN V = 6V IN V = 8.4V IN 60 60 50 50 V = 2.5V V = 2.5V OUT OUT R = 0.03 R = 0.03 SENSE SENSE 40 40 1 10 100 1000 1 10 100 1000 LOAD CURRENT (mA) DC232 BP LOAD CURRENT (mA) DC232G01 DC232G02 1 EFFICIENCY (%) EFFICIENCY (%)DEMO MANUAL DC232 NO-DESIGN SWITCHER WWU W PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS VALUE I Maximum Output Current V = 4.2V, V = 2.5V 1.5A OUT IN OUT V Typical Load Regulation 0mA < I < 1.5A, V = 8.5V 1% OUT OUT IN V Typical Output Ripple I = 1.5A, V = 4.2V, Burst Mode Operation Defeated 40mV RIPPLE OUT IN P-P I = 100mA, V = 4.2V, Burst Mode Operation Enabled 120mV OUT IN P-P f Maximum Synchronizable Frequency V = 2.5V, V 8.5V 750kHz SYNC OUT IN V = 1.8V, V 7V 600kHz OUT IN PACKAGE A D SCHE ATIC DIAGRA SM V IN TOP VIEW 2V TO SENSE 1 8 V C1 IN R2 8.5V 10F I 2 7 PDRV 1 8 0.03 TH SENSE V 10V IN V 3 6 GND FB RUN/SS 4 5 SYNC/MODE 2 7 I PDRV Si3443DV TH MS8 PACKAGE U1 V 8-LEAD PLASTIC MSOP LTC1622 OUT 3 6 1,8V, 2.5V, C3 V GND FB L1 470pF 3.3V LTC1622 R3 R6 R5 D1 4.7H ADJ2 4 RUN/ RUN/ 237k 158k 499k 5 SYNC/ SS SS MODE/ MODE SYNC + A B C C2 R1 47F 1.8V 2.5V 10k C4 6V C5 3.3/ADJ 470pF 120pF JP1 R4 ADJ1 75k GND DC232 F01 Figure 1. LTC1622 Low Input Voltage Current Mode Step-Down DC/DC Converter Schematic PARTS LIST REFERENCE DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE C1 1 LMK325BJ106K-T 10F 10V Ceramic Capacitor Taiyo Yuden (408) 573-4150 C2 1 6TPA47M 47F 6V POSCAP Capacitor Sanyo (619) 661-6835 C3, C4 1 06035A471KAT 470pF 50V 10% NPO Chip Capacitor AVX (843) 946-0362 C5 1 06035A121KAT 120pF 50V 10% NPO Chip Capacitor AVX (843) 946-0362 D1 1 IR10BQ015 Schottky Diode International Rectifier (310) 322-3331 J1 to J6 6 1502-2 0.09 Turret Connector Keystone (718) 956-8900 JP1 1 22025-6G2 0.079 cc 6-Pin Jumper Comm Con (626) 301-4200 L1 1 LQN6C-4R7 4.7H Inductor Murata (814) 237-1431 M1 1 Si3443DV Sublogic Threshold P-Channel MOSFET Siliconix (800) 554-5565 R1 1 CR16-103J 10k 5% 0.1W 0603 Resistor TAD (800) 508-1521 R2 1 LR1206-01-R030F 0.030 1% 0.25W 1206 Resistor IRC (512) 992-7900 R3 1 CR16-2373FM 237k 1% 0.1W 0603 Resistor TAD (800) 508-1521 R4 1 CR16-7502FM 75k 1% 0.1W 0603 Resistor TAD (800) 508-1521 R5 1 CR16-4993FM 499k 1% 0.1W 0603 Resistor TAD (800) 508-1521 R6 1 CR16-1583FM 158k 1% 0.1W 0603 Resistor TAD (800) 508-1521 U1 1 LTC1622CMS8 8-Pin MSOP IC LTC (408) 432-1900 2 W W U