Dynamically Adjustable, Synchronous Step-Down Controller for Notebook CPUs

The MAX1717 step-down controller is intended for core CPU DC-DC converters in notebook computers. It features a dynamically adjustable output, ultra-fast transient response, high DC accuracy, and high efficiency needed for leading-edge CPU core power supplies. Maxim's proprietary Quick-PWM™ quick-response, constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns Instant-on" response to load transients while maintaining a relatively constant switching frequency.

The output voltage can be dynamically adjusted through the 5-bit digital-to-analog converter (DAC) inputs over a 0.925V to 2V range. A unique feature of the MAX1717 is an internal multiplexer (mux) that accepts two 5-bit DAC settings with only five digital input pins. Output voltage transitions are accomplished with a proprietary precision slew-rate control that minimizes surge currents to and from the battery while guaranteeing "just-in-time" arrival at the new DAC setting.

High DC precision is enhanced by a two-wire remote-sensing scheme that compensates for voltage drops in the ground bus and output voltage rail. Alternatively, the remote-sensing inputs can be used together with the MAX1717's high DC accuracy to implement a voltage-positioned circuit that modifies the load-transient response to reduce output capacitor requirements and full-load power dissipation.

Single-stage buck conversion allows these devices to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, two-stage conversion (stepping down the +5V system supply instead of the battery) at a higher switching frequency allows the minimum possible physical size.

The MAX1717 is available in a 24-pin QSOP package.

Applications

* 2-Cell to 4-Cell Li+ Battery to CPU Core Supply Converters * 5V to CPU Core Supply Converters * Notebook Computers with Intel SpeedStep® or Other Dynamically Adjustable Processors

* Quick-PWM Architecture

* ±1% VOUT Accuracy Over Line and Load

* 5-Bit On-Board DAC with Input Mux

* Precision-Adjustable VOUT Slew Control

* 0.925V to 2V Output Adjust Range

* Supports Voltage-Positioned Applications

* 2V to 28V Battery Input Range

* Requires a Separate +5V Bias Supply

* 200/300/550/1000kHz Switching Frequency

* Over/Undervoltage Protection

* Drives Large Synchronous-Rectifier FETs

* 700µA (typ) ICC Supply Current

* 2µA (typ) Shutdown Supply Current

* 2V ±1% Reference Output

* VGATE Transition-Complete Indicator

* Small 24-Pin QSOP Package