LTC1627 Monolithic Synchronous Step-Down Switching Regulator FEATURES DESCRIPTIO n High Efficiency: Up to 96% The LTC 1627 is a monolithic current mode synchronous n Constant Frequency 350kHz Operation buck regulator using a fixed frequency architecture. The n 2.65V to 8.5V V Range IN operating supply range is from 8.5V down to 2.65V, making n V from 0.8V to V , I to 500mA OUT IN OUT it suitable for one or two lithium-ion battery-powered appli- n No Schottky Diode Required cations. Burst Mode operation provides high efficiency at n Synchronizable Up to 525kHz low load currents. 100% duty cycle provides low dropout TM n Selectable Burst Mode Operation operation, which extends operating time in battery-operated n Low Dropout Operation: 100% Duty Cycle systems. n Precision 2.5V Undervoltage Lockout n The operating frequency is internally set at 350kHz, allowing Secondary Winding Regulation n the use of small surface mount inductors. For switching noise Current Mode Operation for Excellent Line and sensitive applications it can be externally synchronized up to Load Transient Response n Low Quiescent Current: 200m A 525kHz. The SYNC/FCB control pin guarantees regulation of n Shutdown Mode Draws Only 15m A Supply Current secondary windings regardless of load on the main output by n 1.5% Reference Accuracy forcing continuous operation. Burst Mode operation is inhib- n Available in 8-Lead SO Package ited during synchronization or when the SYNC/FCB pin is U pulled low to reduce noise and RF interference. Soft-start is APPLICATIO S provided by an external capacitor. n Cellular Telephones Optional bootstrapping enhances the internal switch drive for n Portable Instruments single lithium-ion cell applications. The internal synchronous n Wireless Modems switch increases efficiency and eliminates the need for an n RF Communications external Schottky diode, saving components and board n Distributed Power Systems space. The LTC1627 comes in an 8-lead SO package. n Scanners , LTC and LT are registered trademarks of Linear Technology Corporation. n Burst Mode is a trademark of Linear Technology Corporation. Single and Dual Cell Lithium 100 TYPICAL APPLICATIO V = 3.3V OUT V = 3.6V IN 95 1 8 V = 6V IN I SYNC/FCB TH 47pF 90 2 7 RUN/SS V DR C SS LTC1627 0.1F V IN 85 V = 8.4V 3 6 IN 2.8V* V V FB IN TO 8.5V L1 15H 4 5 + C 80 V IN OUT GND SW 22F 3.3V + C OUT 16V 100F 75 249k 6.3V 70 1 10 100 1000 *V CONNECTED TO V FOR 2.8V < V < 3.3V OUT IN IN 80.6k OUTPUT CURRENT (mA) 1627 F01a 1627 F01b Figure 1a. High Efficiency Step-Down Converter Figure 1b. Efficiency vs Output Load Current 1 EFFICIENCY (%) U ULTC1627 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage ................................ 0.3V to 10V ORDER PART TOP VIEW NUMBER Driver Supply Voltage (V V ) ........... 0.3V to 10V IN DR I 1 8 SYNC/FCB TH I Voltage .................................................. 0.3V to 5V TH RUN/SS 2 7 V DR LTC1627CS8 Run/SS, V Voltages ................................ 0.3V to V FB IN V 3 6 V LTC1627IS8 FB IN Sync/FCB Voltage ...................................... 0.3V to V IN GND 4 5 SW V Voltage (V 5V) ............................... 5V to 0.3V DR IN S8 PART MARKING P-Channel Switch Source Current (DC) .............. 800mA S8 PACKAGE 8-LEAD PLASTIC SO N-Channel Switch Sink Current (DC) .................. 800mA 1627 Peak SW Sink and Source Current ......................... 1.5A T = 125 C, q = 110 C/ W JMAX JA 1627I Operating Ambient Temperature Range Consult factory for Military grade parts. Commercial ............................................ 0 C to 70 C Industrial ........................................... 40 C to 85 C 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) 20 60 nA VFB V Regulated Feedback Voltage (Note 3) l 0.788 0.80 0.812 V FB D V D Output Overvoltage Lockout D V = V V 20 60 110 mV OVL OVL OVL FB D V Reference Voltage Line Regulation V = 2.8V 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 Synchronized V = 8.5V, V = 3.3V, Frequency = 525kHz 450 m A IN OUT Burst Mode Operation V = 0V, V = 8.5V, V = Open 200 320 m A ITH IN SYNC/FCB Shutdown V = 0V, 2.65V < V < 8.5V 15 35 m A RUN/SS IN Shutdown V = 0V, V < 2.65V 6 m A RUN/SS IN V Run/SS Threshold 0.4 0.7 1.0 V RUN/SS I Soft-Start Current Source V = 0V 1.2 2.25 3.3 m A RUN/SS RUN/SS V Auxiliary Feedback Threshold V Ramping Negative 0.730 0.8 0.860 V SYNC/FCB SYNC/FCB I Auxiliary Feedback Current V = 0V 0.5 1.5 2.5 m A SYNC/FCB SYNC/FCB f Oscillator Frequency V = 0.8V 315 350 385 kHz OSC FB V = 0V 35 kHz FB V Undervoltage Lockout V Ramping Down from 3V (40 C to 85 C) 2.3 2.50 2.65 V UVLO IN V Ramping Up from 0V (40 C to 85 C) 2.65 2.85 V IN V Ramping Down from 3V (0 C to 70 C) 2.4 2.50 2.65 V IN V Ramping Up from 0V (0 C to 70 C) 2.65 2.80 V IN R R of P-Channel FET (V V ) = 5V, I = 100mA 0.5 0.7 W PFET DS(ON) IN DR SW R R of N-Channel FET I = 100mA 0.6 0.8 W NFET DS(ON) SW I SW Leakage V = 0V 10 1000 nA LSW RUN/SS Note 1: Absolute Maximum Ratings are those values beyond which the life Note 3: The LTC1627 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 is calculated from the ambient temperature T and power Note 2: T 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