High-Speed, Digitally Adjusted Step-Down Controllers for Notebook CPUs

The MAX1710/MAX1711 step-down controllers are intended for core CPU DC-DC converters in notebook computers. They feature a triple-threat combination of 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.

High DC precision is ensured by a 2-wire remote-sensing scheme that compensates for voltage drops in both the ground bus and supply rail. An on-board, digital-to-analog converter (DAC) sets the output voltage in compliance with Mobile Pentium II® CPU specifications.

The MAX1710 achieves high efficiency at a reduced cost by eliminating the current-sense resistor found in traditional current-mode PWMs. Efficiency is further enhanced by an ability to drive very large synchronous-rectifier MOSFETs.

Single-stage buck conversion allows these devices to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, 2-stage conversion (stepping down the +5V system supply instead of the battery) at a higher switching frequency allows the minimum possible physical size.

The MAX1710/MAX1711 are identical except that the MAX1711 have 5-bit DACs and the MAX1710 has a 4-bit DAC. Also, the MAX1711 has a fixed overvoltage protection threshold at VOUT = 2.25V and undervoltage protection at VOUT = 0.8V whereas the MAX1710 has variable thresholds that track VOUT. The MAX1711 is intended for applications where the DAC code may change dynamically.

Applications

* CPU Core DC-DC Converters * Docking Stations * Notebook Computers * Single-Stage (BATT to VCORE) Converters * Two-Stage (+5V to VCORE) Converters

* Ultra-High Efficiency

* No Current-Sense Resistor (Lossless ILIMIT)

* Quick-PWM with 100ns Load-Step Response

* ±1% VOUT Accuracy over Line and Load

* 4-Bit On-Board DAC (MAX1710)

* 5-Bit On-Board DAC (MAX1711/MAX1712)

* 0.925V to 2V Output Adjust Range (MAX1711/MAX1712)

* 2V to 28V Battery Input Range

* 200/300/400/550kHz Switching Frequency

* Remote GND and VOUT Sensing

* Over/Undervoltage Protection

* 1.7ms Digital Soft-Start

* Drive Large Synchronous-Rectifier FETs

* 2V ±1% Reference Output

* Power-Good Indicator

* Small 24-Pin QSOP Package