DEMO MANUAL DC257 NO-DESIGN SWITCHER LTC1707 Monolithic Synchronous Step-Down Regulator U DESCRIPTIO Demonstration circuit DC257 is a constant-frequency it ideal for single lithium-ion battery applications. DC257s step-down converter using an LTC 1707 monolithic syn- output voltage is programmable from 1.5V to 3.3V via a chronous regulator. It provides low input voltage, high jumper. conversion efficiency for cell phones and other portable At low output currents, the LTC1707 automatically switches electronics operating from one or two Li-Ion cells or three TM to Burst Mode operation to reduce switching losses and to six NiCd cells. Constant 350kHz operation and up to maintain high operating efficiencies. In switching-noise 600mA output capability in an SO-8 package provide a low sensitive applications, Burst Mode operation can be inhib- noise, space-efficient solution for wireless applications. ited by grounding the SYNC/MODE pin or synchronizing it The circuit highlights the capability of the LTC1707. De- with an external clock. Gerber files for this circuit board signed to work at low voltages, the input voltage (V ) can are available. Call the LTC factory. IN range from 2.85V to 8.5V. At V < 2.7V, the LTC1707 IN , LTC and LT are registered trademarks of Linear Technology Corporation. shuts down and draws just a few microamperes, making Burst Mode is a trademark of Linear Technology Corporation. WWU W PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS JUMPER POSITION VALUE V Input Voltage Range 2.85V to 8.5V IN V Output Voltage See Figure 2 JP1 = 1.5V 1.51V 0.036V OUT JP1 = 1.8V 1.82V 0.043V JP1 = 2.5V 2.52V 0.06V JP1 = 2.9V 2.94V 0.07V JP1 = 3.3V 3.33V 0.079V JP1 = OPEN Note 1 I Pulse Skipping Mode Supply Current V = 5V, SYNC/MODE = 0V, RUN/SS = 2V, I = 0mA JP1 = 3.3V 300m A Q IN OUT Burst Mode Enabled Supply Current V = 5V, SYNC/MODE = 2V, RUN/SS = 2V, I = 0mA JP1 = 3.3V 200m A IN OUT Shutdown Current V = 5V, RUN/SS = 0V, I = 0mA JP1 = 3.3V 15m A IN OUT W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO LTC1707 Efficiency Curve Demo Board 100 V = 3.3V OUT V = 3.6V IN 95 V = 6V IN 90 85 V = 8.4V IN 80 75 70 1 10 100 1000 OUTPUT CURRENT (mA) DC257 TA01 1 EFFICIENCY (%)DEMO MANUAL DC257 NO-DESIGN SWITCHER PERFOR A CE SU ARY SYMBOL PARAMETER CONDITIONS JUMPER POSITION VALUE I Minimum Output Current V = 5V, V = 2.5V 600mA OUT IN OUT V = 5V, V = 3.3V 500mA IN OUT V = 3V, V = 2.5V 300mA IN OUT f Operating Frequency Unsynchronized All 350kHz OSC Synchronized All 385kHz to 550kHz V Typical Output Ripple I = 500mA, V = 5V, V = 3.3V 30mV RIPPLE OUT IN OUT P-P V Typical Load Regulation 0mA < I < 0.5A, V = 5V, V = 3.3V 0.5% OUT OUT IN OUT V Synchronize Threshold Voltage All 1.2V SYNC V Minimum Shutdown Threshold Voltage All 0.4V RUN/SS V Reference Output Voltage I = 0 All 1.19V REF REF I Maximum V Output Currrent All 100m A REF REF Note 1: Programmable via optional R6. V = 0.8V(1 + 210k/R6) OUT PACKAGE A D SCHE ATIC DIAGRA S TOP VIEW I 1 8 V TH REF RUN/SS 2 7 SYNC/MODE C V V C2 3 6 FB IN 47pF GND 4 5 SW S8 PACKAGE 8-LEAD PLASTIC SO OPTIONAL LTC1707CS8 C C1 R C 1 8 E1 II V THTH REF V REF 2 7 SYNC/ E8 RUN/SS MODE SYNC/MODE LTC1707 C SS 3 6 E2 0.1F V V FB IN V 8.5V IN L1 15H 4 5 E7 GND SW V OUT R7 R8 210k 10 E6 V OSENSE + C + C IN OUT C REF 22F 100F E3 1000pF R1 R2 R3 R4 R5 R6* 16V 6.3V RUN/SS 237k 165k 97.6k 78.7k 66.5k OPTIONAL JP2 1.5V 1.8V 2.5V 3.3V OPEN 2.9V E4/E5 DC257 F01 GND *SPACE IS PROVIDED FOR AN OPTIONAL RESISTOR TO PROGRAM A CUSTOM OUTPUT VOLTAGE. THE OUTPUT VOLTAGE MUST NOT EXCEED 3.3V Figure 1. LTC1707 Constant Frequency, High Efficiency Converter 2 W WU WW U W