LTC1707 High Efficiency Monolithic Synchronous Step-Down Switching Regulator FEATURES DESCRIPTIO n 600mA Output Current (V 4V) The LTC 1707 is a high efficiency monolithic current IN n High Efficiency: Up to 96% mode synchronous buck regulator using a fixed frequency n Constant Frequency: 350kHz Synchronizable architecture. The operating supply range is from 8.5V to 550kHz down to 2.85V, making it suitable for both single and dual n 2.85V to 8.5V V Range IN lithium-ion battery-powered applications. Burst Mode op- n 0.8V Feedback Reference Allows Low Voltage eration provides high efficiency at low load currents. Outputs: 0.8V V V OUT IN 100% duty cycle provides low dropout operation, extend- n No Schottky Diode Required ing operating time in battery-powered systems. n 1.19V 1% Reference Output Pin TM The switching frequency is internally set at 350kHz, n Selectable Burst Mode Operation/Pulse allowing the use of small surface mount inductors. For Skipping Mode n noise sensitive applications it can be externally synchro- Low Dropout Operation: 100% Duty Cycle n nized up to 550kHz. Burst Mode operation is inhibited Precision 2.7V Undervoltage Lockout n during synchronization or when the SYNC/MODE pin is Current Mode Control for Excellent Line and Load Transient Response pulled low preventing low frequency ripple from interfer- n Low Quiescent Current: 200m A ing with audio circuitry. Soft-start is provided by an n Shutdown Mode Draws Only 11m A Supply Current external capacitor. n Available in 8-Lead SO Package The internal synchronous MOSFET switch increases effi- U ciency and eliminates the need for an external Schottky APPLICATIO S diode, saving components and board space. Low output n Cellular Telephones voltages down to 0.8V are easily achieved due to the 0.8V n Portable Instruments internal reference. The LTC1707 comes in an 8-lead SO n Wireless Modems package. n RF Communications , LTC and LT are registered trademarks of Linear Technology Corporation. n Distributed Power Systems Burst Mode is a trademark of Linear Technology Corporation. n Single and Dual Cell Lithium TYPICAL APPLICATIO 100 V = 3.3V OUT V = 3.6V IN 95 V = 6V IN 90 15H V * IN 6 5 V OUT 3V TO V SW IN 85 V = 8.4V 3.3V IN + + 8.5V 100F 22F 2 8 249k 6.3V RUN V REF 16V 80 LTC1707 7 3 SYNC/MODE V FB 75 80.6k 1 I TH GND 70 47pF 1 10 100 1000 4 *V FOLLOWS V FOR OUT IN OUTPUT CURRENT (mA) 3V < VIN < 3.3V 1707 F01a 1707 F01b Figure 1a. High Efficiency Low Dropout Step-Down Converter Figure 1b. Efficiency vs Output Load Current 1 EFFICIENCY (%) U ULTC1707 UU W ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage ................................ 0.3V to 10V ORDER PART TOP VIEW NUMBER I Voltage ................................................. 0.3V to 5V TH RUN/SS, V Voltages ............................... 0.3V to V I 1 8 V FB IN TH REF LTC1707CS8 SYNC/MODE Voltage ................................. 0.3V to V RUN/SS 2 7 SYNC/MODE IN LTC1707IS8 P-Channel Switch Source Current (DC) .............. 800mA V 3 6 V FB IN N-Channel Switch Sink Current (DC) .................. 800mA GND SW 4 5 S8 PART MARKING Peak SW Sink and Source Current ......................... 1.5A S8 PACKAGE Operating Ambient Temperature Range 8-LEAD PLASTIC SO 1707 T = 125 C, q = 120 C/ W JMAX JA Commercial ............................................ 0 C to 70 C 1707I Industrial ........................................... 40 C to 85 C Consult factory for Military grade parts. Junction Temperature (Note 2)............................. 125 C Storage Temperature Range ................ 65 C to 150 C Lead Temperature (Soldering, 10 sec)................. 300 C ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 5V unless otherwise specified. A IN SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I Feedback Current (Note 3) 6 60 nA VFB V Regulated Feedback Voltage (Note 3) l 0.78 0.80 0.82 V FB D V Output Overvoltage Lockout D V = V V 20 60 110 mV OVL OVL OVL FB D V Reference Voltage Line Regulation V = 3V to 8.5V (Note 3) 0.002 0.01 %/V FB IN V Output Voltage Load Regulation I Sinking 2m A (Note 3) 0.5 0.8 % LOADREG TH I Sourcing 2m A (Note 3) 0.5 0.8 % TH I Input DC Bias Current (Note 4) S Pulse Skipping Mode V = 8.5V, V = 3.3V, V = 0V 300 m A IN OUT SYNC/MODE Burst Mode Operation V = 0V, V = 8.5V, V = Open 200 320 m A ITH IN SYNC/MODE Shutdown V = 0V, 3V < V < 8.5V 11 35 m A RUN/SS IN Shutdown V = 0V, V < 3V 6 m A RUN/SS IN V Run/SS Threshold V Ramping Positive 0.4 0.7 1.0 V RUN/SS RUN/SS I Soft-Start Current Source V = 0V 1.2 2.25 3.3 m A RUN/SS RUN/SS I SYNC/MODE Pull-Up Current V = 0V 0.5 1.5 2.5 m A SYNC/MODE SYNC/MODE f Oscillator Frequency V = 0.7V 315 350 385 kHz OSC FB = 0V 35 kHz V FB V Undervoltage Lockout V Ramping Down from 3V (0 C to 70 C) 2.55 2.70 2.85 V UVLO IN V Ramping Up from 0V (0 C to 70 C) 2.60 2.80 3.00 V IN V Ramping Down from 3V (40 C to 85 C) 2.45 2.70 2.85 V IN V Ramping Up from 0V (40 C to 85 C) 2.50 2.80 3.00 V IN R R of P-Channel FET I = 100mA 0.5 0.7 W PFET DS(ON) SW R R of N-Channel FET I = 100mA 0.6 0.8 W NFET DS(ON) SW I Peak Inductor Current V = 4V, I = 1.4V, Duty Cycle < 40% 0.70 0.915 1.10 A PK IN TH I SW Leakage V = 0V 10 1000 nA LSW RUN/SS V Reference Output Voltage I = 0m A l 1.178 1.19 1.202 mV REF REF D V Reference Output Load Regulation 0V I 100m A l 2.3 15 mV REF REF Note 1: Absolute Maximum Ratings are those values beyond which the life Note 3: The LTC1707 is tested in a feedback loop that servos V to the FB of a device may be impaired. balance point for the error amplifier (V = 0.8V). ITH Note 2: T is calculated from the ambient temperature T and power Note 4: Dynamic supply current is higher due to the gate charge being J A dissipation P according to the following formula: delivered at the switching frequency. D T = T + (P 110 C/W) J A D 2 U WWW