MAX797H 19-1239 Rev 0 7/97 High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power General Description Features The MAX797H high-performance, step-down DC-DC 96% Efficiency converter provides main CPU power in battery-powered Up to 40V Power Input systems. A 40V rating on the power stages input allows 2.5V to 6V Adjustable Output operation with high-cell-count batteries and a wide range of AC adaptors. This buck controller achieves Preset 3.3V and 5V Outputs (at up to 10A) 96% efficiency by using synchronous rectification and 5V Linear-Regulator Output Maxims proprietary Idle Mode control scheme to Precision 2.505V Reference Output extend battery life at full-load (up to 10A) and no-load outputs. Excellent dynamic response corrects output tran- Automatic Bootstrap Circuit sients caused by the latest dynamic-clock CPUs within five 150kHz/300kHz Fixed-Frequency PWM Operation 300kHz clock cycles. Unique bootstrap circuitry drives Programmable Soft-Start inexpensive N-channel MOSFETs, reducing system cost and eliminating the crowbar switching currents found in 375A Quiescent Current (V = 12V, V = 5V) IN OUT some PMOS/NMOS switch designs. 1A Shutdown Current The MAX797H has a logic-controlled and synchronizable fixed-frequency, pulse-width-modulating (PWM) operating Ordering Information mode, which reduces noise and RF interference in sensi - tive mobile-communications and pen-entry applications. PART TEMP. RANGE PIN-PACKAGE The SKIP override input allows automatic switchover to MAX797HESE -40C to +85C 16 Narrow SO idle-mode operation (for high-efficiency pulse skipping) at U light loads, or forces fixed-frequency mode for lowest noise at all loads. The MAX797H is pin compatible with the popu- lar MAX797, but has a higher input voltage range. Typical Operating Circuit The MAX797H comes in a 16-pin narrow SO package. +4V TO +40V +4.5V TO +30V Applications POWER INPUT SUPPLY INPUT Notebook and Subnotebook Computers Industrial Controls V+ VL SHDN Pin Configuration DH +3.3V OUTPUT MAX797H TOP VIEW BST SS 1 16 DH SS LX SKIP 2 15 LX REF 3 14 BST REF DL MAX797H GND 4 13 DL PGND PGND SYNC 5 12 SHDN 6 11 VL SYNC CSH FB 7 10 V+ CSH 8 9 CSL GND CSL SKIP FB SO Idle Mode is a trademark of Maxim Integrated Products. Maxim Integrated Products 1 For free samples & the latest literature: High-Voltage, Step-Down Controller with Synchronous Rectifier for CPU Power ABSOLUTE MAXIMUM RATINGS V+ to GND ................................................................-0.3V to 36V VL Short Circuit to GND..............................................Momentary GND to PGND........................................................................2V REF Short Circuit to GND...........................................Continuous VL to GND...................................................................-0.3V to 7V VL Output Current...............................................................50mA BST to GND ..............................................................-0.3V to 46V Continuous Power Dissipation (T = +70C) A DH to LX .....................................................-0.3V to (BST + 0.3V) SO (derate 8.70mW/C above +70C)........................696mW LX to BST ....................................................................-7V to 0.3V Operating Temperature Range SHDN to GND...........................................................-0.3V to 36V MAX797HESE .................................................-40C to +85C SYNC, SS, REF, FB, SKIP, DL to GND...........-0.3V to (VL + 0.3V) Storage Temperature Range .............................-65C to +160C CSH, CSL to GND.......................................................-0.3V to 7V Lead Temperature (soldering, 10sec) .............................+300C 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+ = 15V, GND = PGND = 0V, I = I = 0A, T = 0C to +85C, SYNC = 0V, unless otherwise noted.) VL REF A PARAMETER CONDITIONS MIN TYP MAX UNITS +3.3V AND +5V STEP-DOWN CONTROLLERS V+ 4.5 30 Input Supply Range V High-side MOSFET drain 40 0mV < (CSH - CSL) < 80mV, FB = VL, 5V Output Voltage (CSL) 6V < power input < 40V, includes line and load 4.85 5.10 5.25 V regulation (Note 4) 0mV < (CSH - CSL) < 80mV, FB = 0V, 3.3V Output Voltage (CSL) 4.5V < power input < 40V, includes line and load 3.20 3.35 3.46 V regulation (Note 4) Nominal Adjustable Output External resistor divider REF 6 V Voltage Range Feedback Voltage CSH - CSL = 0V 2.43 2.505 2.57 V 0mV < (CSH - CSL) < 80mV 2.5 Load Regulation % 25mV < (CSH - CSL) < 80mV 1.5 FB = VL, 6V < power input < 40V (Note 4) 0.04 0.06 Line Regulation %/V FB = 0V, 4.5V < power input < 40V (Note 4) 0.04 0.06 CSH - CSL, positive 80 100 120 Current-Limit Voltage mV CSH - CSL, negative -50 -100 -160 SS Source Current 2.5 4.0 6.5 A SS Fault Sink Current 2.0 mA FLYBACK/PWM CONTROLLERINTERNAL REGULATOR AND REFERENCE VL Output Voltage SHDN = 2V, 0mA < I < 25mA, 5.5V < V+ < 30V 4.7 5.3 V VL VL Fault Lockout Voltage Rising edge, hysteresis = 15mV 3.8 4.1 V VL/CSL Switchover Voltage Rising edge, hysteresis = 25mV 4.2 4.7 V 2 MAX797H