MAX1809 19-2142 Rev 1 9/02 3A, 1MHz, DDR Memory Termination Supply General Description Features The MAX1809 is a reversible energy flow, constant-off- Source/Sink 3A time, pulse-width modulated (PWM), step-down DC-DC 1% Output Accuracy converter. It is ideal for use in notebook and subnote- book computers that require 1.1V to 5V active Up to 1MHz Switching Frequency termination power supplies. This device features an 93% Efficiency internal PMOS power switch and internal synchronous rectifier for high efficiency and reduced component Internal PMOS/NMOS Switches count. The internal 90m PMOS power switch and 90m /70m On-Resistance at V = 4.5V IN 70m NMOS synchronous-rectifier switch easily deliver 110m /80m On-Resistance at V = 3V IN continuous load currents up to 3A. The MAX1809 accu- 1.1V to V Adjustable Output Voltage rately tracks an external reference voltage, produces IN an adjustable output from 1.1V to V and achieves IN, 3V to 5.5V Input Voltage Range efficiencies as high as 93%. <1A Shutdown Supply Current The MAX1809 uses a unique current-mode, constant- off-time, PWM control scheme that allows the output to Programmable Constant-Off-Time Operation source or sink current. This feature allows energy to Thermal Shutdown return to the input power supply that otherwise would be wasted. The programmable constant-off-time archi- Adjustable Soft-Start Inrush Current Limiting tecture sets switching frequencies up to 1MHz, allowing Output Short-Circuit Protection the user to optimize performance trade-offs between efficiency, output switching noise, component size, and cost. The MAX1809 features an adjustable soft-start to Ordering Information limit surge currents during startup, a 100% duty-cycle PART TEMP RANGE PIN-PACKAGE mode for low-dropout operation, and a low-power shut- down mode that disables the power switches and MAX1809EGI* -40C to +85C 28 QFN reduces supply current below 1A. The MAX1809 is MAX1809EEE -40C to +85C 16 QSOP available in a 28-pin QFN with an exposed backside MAX1809ETI -40C to +85C 28 Thin QFN pad, a 28-pin thin QFN, or a 16-pin QSOP. *Contact factory for availability. Applications DDR Memory Termination Pin Configurations Active Termination Buses TOP VIEW Typical Operating Circuit N.C. 1 21 PGND V V IN OUT IN LX IN 2 20 PGND LX LX 3 19 MAX1809 PGND IN 4 18 LX MAX1809 V GND CC N.C. 5 17 PGND FB SHDN V SS 6 16 CC V SET EXTREF REF EXTREF 7 15 GND TOFF SS THIN QFN Pin Configurations continued at end of data sheet. Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com. TOFF 8 28 N.C. FB 9 27 SHDN N.C. N.C. 10 26 LX N.C. 11 25 N.C. 12 24 N.C. 13 23 LX GND 14 22 REF N.C.3A, 1MHz, DDR Memory Termination Supply ABSOLUTE MAXIMUM RATINGS V , IN to GND ........................................................-0.3V to +6V Continuous Power Dissipation (T = +70C) CC A IN to V .............................................................................0.3V 28-Pin QFN (derate 20mW/C above +70C CC 2 GND to PGND.....................................................................0.3V part mounted on 1in of 1oz copper)..............................1.6W SHDN, SS, FB, T , R , 16-Pin QSOP (derate 12.5mW/C above +70C OFF REF 2 EXTREF to GND.......................................-0.3V to (V + 0.3V) part mounted on 1in of 1oz copper).................................1W CC LX Current (Note 1).............................................................4.7A Operating Temperature Range ...........................-40C to +85C REF Short Circuit to GND Duration ............................Continuous Junction Temperature......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Note 1: LX has clamp diodes to PGND and IN. If continuous current is applied through these diodes, thermal limits must be observed. 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 = V = 3.3V, V = 1.1V, T = 0C to +85C, unless otherwise noted. Typical values are at T = +25C.) IN CC EXTREF A A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Voltage V ,V 3.0 5.5 V IN CC Feedback Voltage Accuracy V = V = 3V to 5.5V, I = 0, IN CC LOAD -12 +12 mV (V - V ) V = 1.25V (Note 2) FB EXTREF EXTREF Feedback Load Regulation Error V I = -3A to +3A, V = 1.25V 20 mV FB LOAD EXTREF External Reference Voltage V - V - REF IN V V = V = 3V to 5.5V V EXTREF IN CC Range 0.01 1.7 Reference Voltage V 1.078 1.100 1.122 V REF Reference Load Regulation I = -1A to +10A 0.5 2.0 mV REF V = 4.5V 90 200 PMOS Switch IN R I = 0.5A m PMOS LX On-Resistance V = 3V 110 250 IN V = 4.5V 70 150 NMOS Switch IN R I = 0.5A m NMOS LX On-Resistance V = 3V 80 200 IN Current-Limit Threshold I V > V 3.5 4.1 4.7 A LIMIT IN LX Switching Frequency f (Note 3) 1 MHz SW I f = 500kHz 1 CC SW No Load Supply Current mA I f = 500kHz 16 IN SW Shutdown Supply Current I SHDN = GND, I + I <1 15 A SHDN CC IN Thermal-Shutdown Threshold Hysteresis = 15C 160 C Undervoltage Lockout Threshold V falling, hysteresis = 90mV 2.5 2.6 2.7 V CC FB Input Bias Current I V = V + 0.1V 0 60 250 nA FB FB EXTREF R = 30.1k 0.24 0.30 0.37 TOFF Off-Time t R = 110k 0.9 1.0 1.1 s OFF TOFF R = 499k 3.8 4.5 5.2 TOFF Startup Off-Time 4 x t s OFF On-Time t (Note 3) 0.35 s ON 2 MAX1809