MAX887 19-1142 Rev 0 9/96 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter General Description Features The MAX887 high-efficiency, step-down DC-DC con- 95% Efficiency verter provides an adjustable output from 1.25V to 600mA Output Current 10.5V. It accepts inputs from 3.5V to 11V and delivers 600mA. Operation to 100% duty cycle minimizes Cycle-by-Cycle Current Limiting dropout voltage (300mV typ at 500mA). Synchronous Low-Dropout, 100% Duty-Cycle Operation, rectification reduces output rectifier losses, resulting in efficiency as high as 95%. 300mV at 500mA Fixed-frequency pulse-width modulation (PWM) Internal 0.6 (typ) MOSFET reduces noise in sensitive communications applica- Internal Synchronous Rectifier tions. Using a high-frequency internal oscillator allows tiny surface-mount components to reduce PC board High-Frequency Current-Mode PWM area, and eliminates audio-frequency interference. A External SYNC or Internal 300kHz Oscillator SYNC input allows synchronization to an external clock to avoid interference with sensitive RF and data- Guaranteed 260kHz to 340kHz Internal Oscillator acquisition circuits. Frequency Limits The MAX887 features current-mode operation for supe- 2.5A Shutdown Mode rior load/line-transient response. Cycle-by-cycle current limiting protects the internal MOSFET and rectifier. A low-current (2.5A typ) shutdown mode conserves bat- tery life. Applications Ordering Information Portable Instruments PART TEMP. RANGE PIN-PACKAGE Cellular Phones and Radios MAX887HC/D 0C to +70C Dice* MAX887HESA -40C to +85C 8 SO Personal Communicators *Contact factory for availability. Dice are tested at T = +25C. A Distributed Power Systems Computer Peripherals Typical Operating Circuit Pin Configuration 33H V = 3.3V V = 3.5V to 11V IN OUT TOP VIEW V+ LX R1 47F SHDN 1 8 V+ 47F 0.33F 165k C1 MAX887 100pF 2 FB 7 LX ON MAX887 SHDN OFF SYNC FB REF 3 6 SYNC VL 5 VL 4 GND REF R2 GND 100k 2.2F 0.047F SO V = 1.25V (R1/R2 + 1) OUT Maxim Integrated Products 1 For free samples & the latest literature: 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter ABSOLUTE MAXIMUM RATINGS REF, FB, SYNC, VL to GND..................................... -0.3V to +6V Operating Temperature Ranges V+ to GND............................................................. -0.3V to +12V MAX887HC/D.......................................................0C to +70C SHDN, LX to GND ....................................... -0.3V to (V+ + 0.3V) MAX887HESA...................................................-40C to +85C PGND to GND ...................................................... -0.3V to +0.3V Storage Temperature Range ........................... -65C to +165C Continuous Power Dissipation (T = +70C) Lead Temperature (soldering, 10sec) ............................ +300C A SO (derate 9.09mW/C above +70C) .........................471mW Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (V+ = +7V, PGND = GND = 0V, SHDN = V+, (T = 0C to T ), unless otherwise noted.) A MAX PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Range V+ 3.5 11.0 V Quiescent Supply Current I I = 0mA, SYNC = 3.0V 2.7 4.0 mA V+, PWM OUT (PWM Mode) Quiescent Supply Current I I = 0mA, SYNC = GND 0.2 0.5 mA V+, PFM OUT (PFM Mode) Shutdown Supply Current I 2.5 5 A SHDN = GND V+, SHDN Output Voltage Range V Circuit of Figure 2 1.25 10.50 V OUT, RANGE Load Regulation I = 0mA to 500mA 0.005 %/mA OUT Line Regulation V = 4V to 11V, PWM mode 0.2 %/V IN PWM FB Feedback Threshold V SYNC = 3.0V, PWM duty cycle = 50% 1.225 1.250 1.275 V FB FB Input Current I FB = 1.30V 0.10 A FB SYNC Frequency f 25 440 kHz SYNC SYNC Pulse Width High or Low SYNC, PW 500 ns PWM Maximum Duty Cycle PWM, DUTY SYNC = 3.0V, FB = 1.18V 100 % PWM Switching Frequency f SYNC = 3.0V 260 300 340 kHz OSC High-Side Current Limit I 0.75 1.0 1.40 A LIM+ LX On-Resistance R I = 100mA 0.6 ON, LX LX LX Leakage Current I V+ = 12V, LX = GND to 12V -10 1.0 10 A LXLKG LX Reverse Leakage Current, I 1.0 20 A LXLKGR V+ = floating, LX = 5V, SHDN = GND Regulator Off Undervoltage Lockout V V+ falling 3.0 3.3 V +, UVLO Startup Voltage V V+ rising 3.1 3.5 V +, START SYNC Input High Voltage V 2.5 V IH, SYNC SYNC Input Low Voltage V 0.5 V IL, SYNC SYNC Input Current I SYNC = GND or 3V 1 A IN, SYNC SHDN Input High Voltage V 2.4 V IH, SHDN SHDN Input Low Voltage V 0.8 V IL, SHDN SHDN Input Current, Sinking I SHDN = GND or V+ 1 A IN-, SHDN SHDN Input Capacitance C (Note 1) 10 pF IN, SHDN VL Output Voltage V I = 0mA to 1mA 3.3 V L VL REF Output Voltage V 0A to 30A 1.25 V REF Note 1: Guaranteed by design and not production tested. 2 MAX887