Step-Down Controllers with Synchronous Rectifier for CPU Power

The MAX796/MAX797/MAX799 high-performance, step-down DC-DC converters with single or dual outputs provide main CPU power in battery-powered systems. These buck controllers achieve 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. 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 MAX796/MAX799 are specially equipped with a secondary feedback input (SECFB) for transformer-based dual-output applications. This secondary feedback path improves cross-regulation of positive (MAX796) or negative (MAX799) auxiliary outputs.

The MAX797 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-bar 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.

The MAX796/MAX797/MAX799 are all available in 16-pin DIP and narrow SO packages. See the table below to compare these three converters.

Applications

* Cell Phones * Notebook and Subnotebook Computers * PDAs and Mobile Communicators

* 96% Efficiency

* 4.5V to 30V Input Range

* 2.5V to 6V Adjustable Output

* Preset 3.3V and 5V Outputs (at up to 10A)

* Multiple Regulated Outputs

* +5V Linear-Regulator Output

* Precision 2.505V Reference Output

* Automatic Bootstrap Circuit

* 150kHz/300kHz Fixed-Frequency PWM Operation

* Programmable Soft-Start

* 375µA Typ Quiescent Current (VIN = 12V, VOUT = 5V)

* 1µA Typ Shutdown Current