MAX8597/MAX8598/MAX8599 19-3505 Rev 1 6/05 Low-Dropout, Wide-Input-Voltage, Step-Down Controllers General Description Features Low Dropout with >99.5% Duty Cycle The MAX8597/MAX8598/MAX8599 voltage-mode PWM step-down controllers are designed to operate from a Lossless High-Side Current Limit 4.5V to 28V input supply and generate output voltages Wide 4.5V to 28V Input Range down to 0.6V. A proprietary switching algorithm stretch- Dynamic Output Voltage Adjustment with es the duty cycle to >99.5% for low-dropout design. Adjustable Offset (MAX8597) Unlike conventional step-down regulators using a p- Remote Voltage Sensing for Both Positive and channel high-side MOSFET to achieve high duty cycle, Negative Rails (MAX8597) the MAX8597/MAX8598/MAX8599 drive n-channel MOSFETs resulting in high efficiency and high-current- Tracking Output Through REFIN (MAX8597) capability designs. Adjustable Switching Frequency from 200kHz to 1.4MHz The MAX8597 is available in a 20-pin thin QFN pack- age and is designed for applications that use an analog Adjustable Soft-Start signal to control the output voltage with an adjustable Prebias Startup offset, such as DC fan-speed control. This is achieved Enable and Power-OK (MAX8598/MAX8599) for with an internal uncommitted operational amplifier. The Flexible Sequencing MAX8597 is also targeted for tracking output-voltage 25MHz Error Amplifier applications for chipsets, ASIC and DSP cores, and I/O supplies. The MAX8598/MAX8599 are available in a 16- Adjustable Hiccup Current Limit for Output pin thin QFN package and do not have the uncommitted Short-Circuit Protection operational amplifier, reference input, and reference out- Output Overvoltage Protection (MAX8599) put, but offer an open-drain, power-OK output. Small, Low-Profile Thin QFN Package The MAX8597/MAX8598/MAX8599 allow startup with prebias voltage on the output for applications where a backup supply or a tracking device may charge the Ordering Information output capacitor before the MAX8597/MAX8598/ PART TEMP RANGE PIN-PACKAGE MAX8599 are enabled. In addition, the MAX8599 fea- tures output overvoltage protection. 20 Thin QFN 4mm x 4mm MAX8597ETP -40C to +85C (T2044-3) These controllers also feature lossless high-side peak inductor current sensing, adjustable current limit, and 20 Thin QFN 4mm x 4mm MAX8597ETP+ -40C to +85C hiccup-mode short-circuit protection. Switching fre- (T2044-3) quency is set with an external resistor from 200kHz to 16 Thin QFN 4mm x 4mm 1.4MHz. This wide frequency range combined with a MAX8598ETE -40C to +85C (T1644-4) wide-bandwidth error amplifier enables the loop com- pensation scheme to give the user ample flexibility to 16 Thin QFN 4mm x 4mm MAX8598ETE+ -40C to +85C optimize for cost, size, and efficiency. (T1644-4) 16 Thin QFN 4mm x 4mm MAX8599ETE -40C to +85C Applications (T1644-4) Nonisolated Power Modules 16 Thin QFN 4mm x 4mm MAX8599ETE+ -40C to +85C Variable-Speed DC Fan Power Supplies (T1644-4) (MAX8597) +Denotes lead-free package. Tracking Power Supplies (MAX8597) Chipset Power Supplies Pin Configurations appear 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. EVALUATION KIT AVAILABLELow-Dropout, Wide-Input-Voltage, Step-Down Controllers ABSOLUTE MAXIMUM RATINGS V+, ILIM to GND.....................................................-0.3V to +30V DL to PGND.................................................-0.3V to (V + 0.3V) VL AVL, VL to GND........................................................-0.3V to +6V Continuous Power Dissipation PGND to GND .......................................................-0.3V to +0.3V 16- or 20-Pin Thin QFN FB, EN, POK, AIN-, AIN+, REFIN to GND ................-0.3V to +6V Up to +70C (derate 16.9mW/C above +70C)........1349mW AOUT, REFOUT, FREQ, SS, COMP to Operating Temperature Range ...........................-40C to +85C GND .....................................................-0.3V to (V + 0.3V) Junction Temperature......................................................+150C AVL BST to GND............................................................-0.3V to +36V Storage Temperature Range .............................-65C to +150C DH to LX....................................................-0.3V to (V + 0.3V) Lead Temperature (soldering, 10s) .................................+300C BST LX to GND ........................-2V (-2.5V for less than 50ns) to +30V LX to BST..................................................................-6V to +0.3V 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 = V = V = V = 5V, V = 6V, V = 1V, C = 4.7F, C = 1F, V = V , V = 2.5V, V = V+ VL AVL EN REFIN BST LX VL REFOUT AIN- AOUT AIN+ ILIM V - 0.2V, V = 0.65V, GND = PGND = 0V, C = 0.01F, R = 20k , T = 0C to +85C, typical values are at T = +25C, LX FB SS FREQ A A unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS GENERAL V+ Operating Range 5.5 28.0 V V+/VL Operating Range V+ = VL 4.5 5.5 V V+ Operating Supply Current V = 12V, VL unloaded, no MOSFETs connected, V = 0V 3.4 5.0 mA V+ FB V+ Standby Supply Current V = 12V, VL unloaded, V = 0V 2.0 mA V+ FB VL REGULATOR Output Voltage 5.5V < V < 28V, 1mA < I < 35mA 4.7 5.0 5.3 V V+ LOAD VL Undervoltage-Lockout Rising edge, typical hysteresis = 460mV 4.05 4.2 4.35 V Trip Level Thermal Shutdown Rising temperature, typical hysteresis = 10C +160 C REFERENCE (MAX8597 only) REFOUT Output Voltage I = 150A, V = V = 4.5V or 5.5V 2.49 2.50 2.51 V REFOUT V+ VL REFOUT Load Regulation I = 10A to 1mA 10 mV REFOUT REFOUT Internal Discharge During VL UVLO 15 Switch On-Resistance CURRENT-LIMIT COMPARATOR (all current limits are tested at V = V = 4.5V and 5.5V) V+ VL ILIM Sink Current 1.8V < V < 28V, V = V + 5V 180 200 220 A LX BST LX Comparator Input Offset V = 28V, V = V + 5V -10 +10 mV LX BST LX Voltage Error SOFT-START Soft-Start Source Current V = 100mV 3 5 7 A SS Soft-Start Sink Current V = (0.6V or V ) 3 5 7 A SS REFIN FREQUENCY R = 100k 150 200 240 FREQ Frequency R = 20.0k 800 1000 1200 kHz FREQ R = 14.3k 1100 1400 1700 FREQ 2 MAX8597/MAX8598/MAX8599