500kHz Multi-Output Power-Supply Controllers with High Impedance in Shutdown

The MAX8741/MAX8742 are buck-topology, step-down, switch-mode, power-supply controllers that generate logic-supply voltages in battery-powered systems. These high-performance, dual/triple-output devices include onboard power-up sequencing, power-good signaling with delay, digital soft-start, secondary winding control, lowdropout circuitry, internal frequency-compensation networks, and automatic bootstrapping.

Up to 97% efficiency is achieved through synchronous rectification and Maxim's proprietary Idle Mode™ control scheme. Efficiency is greater than 80% over a 1000:1 load-current range, which extends battery life in system suspend or standby mode. Excellent dynamic response corrects output load transients within five clock cycles. Strong 1A on-board gate drivers ensure fast external n-channel MOSFET switching.

These devices feature a logic-controlled and synchronizable, fixed-frequency, pulse-width-modulation (PWM) operating mode. This reduces noise and RF interference in sensitive mobile communications and pen-entry applications. Asserting the active-low SKIP pin enables fixed-frequency mode, for lowest noise under all load conditions.

The MAX8741/MAX8742 include two PWM regulators, adjustable from 2.5V to 5.5V with fixed 5.0V and 3.3V modes. All these devices include secondary feedback regulation, and the MAX8742 contains a 12V/120mA linear regulator. The MAX8741 includes a secondary feedback input (SECFB), plus a control pin (STEER) that selects which PWM (3.3V or 5V) receives the secondary feedback signal. SECFB provides a method for adjusting the secondary winding voltage regulation point with an external resistor-divider, and is intended to aid in creating auxiliary voltages other than fixed 12V.

The MAX8741/MAX8742 contain internal output overvoltage- and undervoltage-protection features.

Applications

* Desktop CPU Local DC-DC Converters * Notebook and Subnotebook Computers * PDAs and Mobile Communicators

* 97% Efficiency

* 4.2V to 30V Input Range

* 2.5V to 5.5V Dual Adjustable Outputs

* Selectable 3.3V and 5V Fixed or Adjustable Outputs (Dual Mode™)

* 12V Linear Regulator

* Adjustable Secondary Feedback (MAX8741)

* 5V/50mA Linear-Regulator Output

* Precision 2.5V Reference Output

* Programmable Power-Up Sequencing

* Power-Good (active-low RESET) Output

* Output Overvoltage Protection

* Output Undervoltage Shutdown

* 333kHz/500kHz Low-Noise, Fixed-Frequency Operation

* Low-Dropout, 98% Duty-Factor Operation

* 2.5mW Typical Quiescent Power (12V Input, Both SMPSs On)

* 4µA Typical Shutdown Current