DEMO MANUAL DC309 NO-DESIGN SWITCHER LTC1773 Low Input Voltage Synchronous Current Mode Step-Down DC/DC Converter U DESCRIPTIO Demo board DC309 is a step-down (buck) regulator using make the LTC1773 ideal for battery-powered applications. the LTC 1773. The exclusive use of surface mount com- In dropout, the external P-channel MOSFET is turned on ponents results in a highly efficient application in a very continuously (100% duty cycle), providing low dropout small board space. It is ideal for cell phones and other operation when V approaches V . Under light load IN OUT portable electronics operating from one or two Li-Ion cells conditions, efficiency can be improved by activating Burst TM or three to six NiCd cells. DC309 is capable of providing Mode operation, which is done by connecting the SYNC/ 2.5A at an output voltage of 1.8V with an input supply of FCB pin to V or leaving it floating. Tying this pin to ground IN 3.3V. This demo board highlights the capabilities of the will force continuous operation, regardless of the load. LTC1773, which uses a current mode PWM architecture to The SYNC/FCB pin can also be used to synchronize the synchronously drive an external pair of P- and N-channel LTC1773 to frequencies of up to 750kHz. At input voltages power MOSFETs. The result is a high performance power below 2.5V, the LTC1773s undervoltage lockout feature is supply that has low output voltage ripple. A constant activated, shutting down the output. Soft-start is provided operating frequency of 550kHz makes the LTC1773 attrac- by connecting an external capacitor to the RUN/SS pin. tive for noise-sensitive applications while allowing for Gerber files for this circuit board are available. Call the smaller external components such as the inductor and the LTC factory. output capacitor. In addition, its high efficiency over a , LTC and LT are registered trademarks of Linear Technology Corporation. wide load current range and its low quiescent current Burst Mode is a trademark of Linear Technology Corporation. WWU W PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS VALUE V Input Supply Voltage Range V = 1.8V 2.8V to 8.5V IN OUT V Output Voltage I = 1A 3.3V 0.066V OUT OUT I = 1A 2.5V 0.050V OUT I = 1A 1.8V 0.036V OUT I = 1A 1.5V 0.030V OUT W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO Efficiency V = 2.5V OUT 100 SEE FIGURE 1 V = 3.3V IN 90 V = 5V IN 80 V = 8V IN 70 60 50 10 1 100 1000 10,000 OUTPUT CURRENT (mA) DC309 TA01 dc309fa 1 EFFICIENCY (%)DEMO MANUAL DC309 NO-DESIGN SWITCHER PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS VALUE V Feedback Voltage 0.8V 0.012V FB I Supply Current Q Burst Mode Operation V = 5V, I = 0 130m A IN OUT Shutdown V = 5V, V = 0V 10m A IN RUN/SS I Maximum Output Current V = 5V, V = 2.5V (Q1 = Si9801DY) 3A OUT IN OUT D V Typical Load Regulation 0mA < I < 3A, V = 8.5V 1% OUT OUT IN V Typical Output Ripple I = 3A, V = 5V 40mV RIPPLE OUT IN P-P I = 100mA, Burst Mode Operation 60mV OUT P-P f Maximum Synchronizable Frequency V = 2.5V, V 8.5V 750kHz SYNC OUT IN V = 1.8V, V 7V 750kHz OUT IN V = 1.5V, V 6V 750kHz OUT IN U WW PACKAGE A D SCHE ATIC DIAGRA S TOP VIEW I 1 10 SW TH RUN/SS 2 9 SENSE SYNC/FCB 3 8 V IN V 4 7 TG FB GND 5 6 BG MS10 PACKAGE 10-LEAD PLASTIC MSOP LTC1773EMS E2 E3 SYNC/FCB RUN/SS R1 100k E4 + V C1 IN C2 R2 + 2.8V TO 8.5V 47F 47pF 0.025 10V 1206 10TPB47MC E5 U1 C3 3 GND LTC1773EMS R3 220pF 4 Q1B 39k Si9801 1 10 I SW TH L1 56 C4 0.1F 2 9 3H RUN/SS SENSE CDRH6D28-3R0 3 8 E6 R4 SYNC/FCB V IN + V 80.6k 1% OUT 1.5V 4 7 1.5V/1.8V/2.5V/3.3V V TG FB 7 8 R5 5 6 2 2.5A AVE/3A PK Q1A JP1 GND BG 196k 1% Si9801 HEADER 3 2 1 1.8V R6 1 2 C6 D2* 57.6k 1% 2.5V 4.7F MBRM120T3 3 4 6.3V POWERMITE 3.3V R7 R8 0805 5 6 31.6k 1% 71.5k 1% C9 C5 + C8 1F 150F 10pF 6.3V 4V X5R 4TPB150MC E7 GND DC309 SD *D2 OPTIONAL Figure 1. LTC1773 Low Input Voltage Synchronous Current Mode Step-Down DC/DC Converter dc309fa 2 WW U W