MAX798 19-1175 Rev 0 12/96 High-Accuracy Step-Down Controller with Synchronous Rectifier for CPU Power General Description Features The MAX798 high-performance, step-down DC-DC 96% Efficiency converter provides main CPU power in battery-powered 4.5V to 30V Input Range systems. This buck controller achieves 96% efficiency 1.6V to 6V Adjustable Precision Output by using synchronous rectification and Maxims propri- etary Idle Mode control scheme to extend battery life 0.4% Max Total Load-Regulation Error at full-load (up to 10A) and no-load outputs. The 0.06%/V Max Line-Regulation Error MAX798s high accuracy meets the demanding require- 5V Linear-Regulator Output ments of the latest-generation CPUs. Excellent dynamic response corrects output transients caused by the latest Precision 2.505V Reference Output dynamic-clock CPUs within five 300kHz clock cycles. Automatic Bootstrap Circuit Unique bootstrap circuitry drives inexpensive N-channel 150kHz/300kHz Fixed-Frequency PWM Operation MOSFETs, reducing system cost and eliminating the crow - bar switching currents found in some PMOS/NMOS switch Programmable Soft-Start designs. 1.2mA Typical Quiescent Current The MAX798 has a logic-controlled and synchronizable (V = 12V, V = 2.5V) IN OUT fixed-frequency pulse-width-modulating (PWM) operating 1A Typical Shutdown Current mode, which reduces noise and RF interference in sensi - tive mobile-communications and pen-entry applications. The SKIP override input allows automatic switchover to Ordering Information idle-mode operation (for high-efficiency pulse skipping) at light loads, or forces fixed-frequency mode for lowest noise PART TEMP. RANGE PIN-PACKAGE at all loads. MAX798ESE -40C to +85C 16 Narrow SO Applications Notebook and Subnotebook Computers Typical Operating Circuit PDAs and Mobile Communicators INPUT 4.5V TO 30V Pin Configuration 5V, 25mA 4.7F TOP VIEW V+ VL BST N DH SS 16 DH 1 R SENSE SKIP 2 15 LX V OUT 0.1F MAX798 REF BST 3 14 LX GND MAX798 DL 4 13 N ON DL SHDN SYNC 5 12 PGND OFF PGND VL SHDN 6 11 FB 7 10 V+ CSH 9 CSH 8 CSL CSL SO FB GND Idle Mode is a trademark of Maxim Integrated Products. U Maxim Integrated Products 1 For free samples & the latest literature: High-Accuracy Step-Down Controller with Synchronous Rectifier for CPU Power ABSOLUTE MAXIMUM RATINGS V+ to GND.................................................................-0.3V, +36V REF Short Circuit to GND...........................................Continuous GND to PGND........................................................................2V VL Output Current...............................................................50mA VL to GND ...................................................................-0.3V, +7V Continuous Power Dissipation (T = +70C) A BST to GND...............................................................-0.3V, +36V SO (derate 8.70mW/C above +70C)........................696mW DH to LX ........................................................-0.3V, (BST + 0.3V) Operating Temperature Range LX to BST.....................................................................-7V, +0.3V MAX798ESE....................................................-40C to +85C SHDN to GND............................................................-0.3V, +36V Storage Temperature Range .............................-65C to +160C SYNC, SS, REF, SKIP, DL to GND...................-0.3V, (VL + 0.3V) Lead Temperature (soldering, 10sec) .............................+300C CSH, CSL to GND .......................................................-0.3V, +7V VL Short Circuit to GND..............................................Momentary 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, unless otherwise noted.) VL REF A PARAMETER CONDITIONS MIN TYP MAX UNITS STEP-DOWN CONTROLLER Input Supply Range 4.5 30 V Nominal Adjustable Output External resistor divider 1.6 6 V Voltage Range Feedback Voltage CSH - CSL = 40mV, SKIP = VL 1.576 1.6 1.624 V Load Regulation 0.4 % 0mV < (CSH - CSL) < 80mV, SKIP = VL Line Regulation 6V < V+ < 30V 0.04 0.05 %/V CSH - CSL, positive 80 100 120 Current-Limit Voltage mV CSH - CSL, negative -40 -100 -160 SS Source Current 2.0 4.0 6.5 A SS Fault Sink Current 2.0 mA INTERNAL REGULATOR AND REFERENCE VL Output Voltage SHDN = 2V, 0mA <I < 25mA, 5.5V < V+ < 30V 4.75 5.25 V VL VL Fault Lockout Voltage Rising edge, hysteresis = 15mV 3.8 4.0 V VL/CSL Switchover Voltage Rising edge, hysteresis = 25mV 4.2 4.7 V Reference Output Voltage No external load (Note 1) 2.463 2.505 2.537 V Reference Fault Lockout Voltage Falling edge 1.8 2.3 V Reference Load Regulation 0A < I < 100A 20 mV REF CSL Shutdown Leakage Current SHDN = 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V 0.1 1 A V+ Shutdown Current 15 A SHDN = 0V, V+ = 30V, CSL = 0V or 6V V+ Off-State Leakage Current FB = CSH = CSL = 6V, VL switched over to CSL 15 A Dropout Power Consumption V+ = 4V, CSL = 0V (Note 2) 6.6 10.5 mW Quiescent Power Consumption CSH = CSL = 6V 6.4 8.5 mW 2 MAX798