High-Accuracy Step-Down Controller with Synchronous Rectifier for CPU Power

The MAX798 high-performance, step-down DC-DC converter provides main CPU power in battery-powered systems. This buck controller achieves 96% efficiency by using synchronous rectification and Maxim's proprietary Idle Mode™ control scheme to extend battery life at full-load (up to 10A) and no-load outputs. The MAX798's high accuracy meets the demanding requirements of the latest-generation CPUs. Excellent dynamic response corrects output transients caused by the latest dynamic-clock CPUs within five 300kHz clock cycles. Unique bootstrap circuitry drives inexpensive N-channel MOSFETs, reducing system cost and eliminating the crowbar switching currents found in some PMOS/NMOS switch designs.

The MAX798 has a logic-controlled and synchronizable fixed-frequency pulse-width-modulating (PWM) operating mode, which reduces noise and RF interference in sensitive mobile-communications and pen-entry applications. The SKIP override input allows automatic switchover to idle-mode operation (for high-efficiency pulse skipping) at light loads, or forces fixed-frequency mode for lowest noise at all loads.

Applications

* Notebook and Subnotebook Computers * PDAs and Mobile Communicators

* 96% Efficiency

* 4.5V to 30V Input Range

* 1.6V to 6V Adjustable Precision Output

* ±0.4% Max Total Load-Regulation Error

* 0.06%/V Max Line-Regulation Error

* 5V Linear-Regulator Output

* Precision 2.505V Reference Output

* Automatic Bootstrap Circuit

* 150kHz/300kHz Fixed-Frequency PWM Operation

* Programmable Soft-Start

* 1.2mA Typical Quiescent Current (VIN = 12V, VOUT = 2.5V)

* 1µA Typical Shutdown Current