LTC1874 Dual Constant Frequency Current Mode Step-Down DC/DC Controller FEATURES DESCRIPTIO n High Efficiency: Up to 94% The LTC 1874 is a dual constant frequency current mode n High Output Currents Easily Achieved step-down DC/DC controller with excellent AC and DC load n Wide V Range: 2.5V to 9.8V and line regulation. Each controller has an accurate IN n Constant Frequency 550kHz Operation undervoltage lockout that shuts down the individual con- TM n Burst Mode Operation at Light Load troller when the input voltage falls below 2.0V. n Low Dropout: 100% Duty Cycle The LTC1874 boasts 2.5% output voltage accuracy and n 0.8V Reference Allows Low Output Voltages consumes only 270m A of quiescent current per controller. n Current Mode Operation for Excellent The LTC1874 is configured with Burst Mode operation, Line and Load Transient Response which enhances efficiency at low output current for appli- n Low Quiescent Current: 270m A (Each Controller) cations where efficiency is a prime consideration. n Separate Shutdown Pin for Each Controller n To further maximize the life of a battery source, each Shutdown Mode Draws Only external P-channel MOSFET is turned on continuously in 8m A Supply Current (Each Controller) dropout (100% duty cycle). In shutdown, each controller n 2.5% Reference Accuracy n draws a mere 8m A. High constant operating frequency of Available in 16-Lead Narrow SSOP n 550kHz allows the use of small external inductors. Each Controller Functions Independent of the Other U The LTC1874 is available in a small footprint 16-lead APPLICATIO S narrow SSOP. n , LTC and LT are registered trademarks of Linear Technology Corporation. 1- or 2-Cell Lithium-Ion-Powered Applications Burst Mode is a trademark of Linear Technology Corporation. n Personal Information Appliances n Portable Computers n Distributed 3.3V, 2.5V or 1.8V Power Systems TYPICAL APPLICATION V IN 3.5V C TO 9.5V IN R1 R2 10F LTC1874 0.04 0.04 1 8 16V V PV IN1 IN2 2 2 7 L2 SENSE1 PGATE2 M2 4.7H V OUT2 3 6 L1 M1 GND1 PGND2 1.8V 4.7H V OUT1 10k 4 5 + C2 1A 3.3V V I /RUN2 D2 FB1 TH 47F 10k 1A + 13 12 220pF C1 6V D1 I /RUN1 V TH FB2 47F 220pF 14 11 C1, C2: SANYO POSCAP 6TPA47M 6V PGND1 GND2 249k C : TAIYO YUDEN CERAMIC IN 15 10 EMK325BJ106MNT ( 2) 100k PGATE1 SENSE2 D1, D2: MBRM120 16 9 80.6k PV V L1, L2: COILCRAFT D01608C-472 IN1 IN2 M1, M2: Si3443DV 80.6k R1, R2: DALE 0.25W 1874 TA01 Figure 1. LTC1874 3.5V-9.5V Input to 3.3V/1A and 1.8V/1A Dual Step-Down Converter 1 U ULTC1874 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) TOP VIEW Input Supply Voltage (V , PV ) ...............0.3V to 10V ORDER PART IN IN SENSE , PGATE Voltages ............. 0.3V to (V + 0.3V) V 1 16 PV NUMBER IN1 IN1 IN SENSE1 2 15 PGATE1 V , I /RUN Voltages ..............................0.3V to 2.4V FB TH GND1 3 LTC1874EGN 14 PGND1 PGATE Peak Output Current (<10m s) ....................... 1A V 4 13 I /RUN1 FB1 TH Storage Ambient Temperature Range ... 65 C to 150 C I /RUN2 5 12 V TH FB2 Operating Temperature Range (Note 2) .. 40 C to 85 C PGND2 6 11 GND2 Junction Temperature (Note 3)............................. 150 C GN PART MARKING PGATE2 7 10 SENSE2 Lead Temperature (Soldering, 10 sec).................. 300 C PV 8 9 V IN2 IN2 1874 GN PACKAGE 16-LEAD NARROW PLASTIC SSOP T = 150 C, q = 135 C/ W JMAX JA Consult factory for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS All specifications apply to each controller. The l denotes specifications that apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 4.2V unless otherwise specified. A IN (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS Input DC Supply Current (Per Controller) Typicals at V = 4.2V (Note 4) IN Normal Operation 2.4V V 9.8V 270 420 m A IN 9.8V 230 370 m A Sleep Mode 2.4V V IN Shutdown 2.4V V 9.8V, V /RUN = 0V 8 22 m A IN ITH UVLO V < UVLO Threshold 6 10 m A IN Undervoltage Lockout Threshold V Falling l 1.55 2.0 2.35 V IN V Rising 1.85 2.3 2.40 V IN Shutdown Threshold (at I /RUN) l 0.15 0.35 0.55 V TH Start-Up Current Source V /RUN = 0V 0.25 0.5 0.85 m A ITH Regulated Feedback Voltage T = 0 C to 70 C (Note 5) l 0.780 0.800 0.820 V A T = 40 C to 85 C (Note 5) l 0.770 0.800 0.830 V A Output Voltage Line Regulation 2.4V V 9.8V (Note 5) 0.05 mV/V IN Output Voltage Load Regulation I /RUN Sinking 5m A (Note 5) 2.5 mV/m A TH I /RUN Sourcing 5m A (Note 5) 2.5 mV/m A TH V Input Current (Note 5) 10 50 nA FB Overvoltage Protect Threshold Measured at V 0.820 0.860 0.895 V FB Overvoltage Protect Hysteresis 20 mV Oscillator Frequency V = 0.8V 500 550 650 kHz FB V = 0V 120 kHz FB Gate Drive Rise Time C = 3000pF 40 ns LOAD Gate Drive Fall Time C = 3000pF 40 ns LOAD Peak Current Sense Voltage (Note 6) 120 mV Note 1: Absolute Maximum Ratings are those values beyond which the life Note 4: Dynamic supply current is higher due to the gate charge being of a device may be impaired. delivered at the switching frequency. Note 2: The LTC1874E is guaranteed to meet performance specifications Note 5: Each controller in the LTC1874 is individually tested in a feedback from 0 C to 70 C. Specifications over the 40 C to 85 C operating loop that servos V to the output of the error amplifier. FB temperature range are assured by design, characterization and correlation Note 6: Peak current sense voltage is reduced dependent upon duty cycle with statistical process controls. to a percentage of value as given in Figure 2. Note 3: T is calculated from the ambient temperature T and power J A dissipation P according to the following formula: D T = T + (P q C/W) J A D JA 2 U W U W U WW