National Semiconductor Corp. (Santa Clara, CA) introduced the LM2637 and LM2638 power-supply voltage controllers designed to be fully compliant with the latest VRM dc/dc converter specification for Whitney or Camino-based PC motherboards. Each controller integrates a 5-bit synchronous step-down switching controller and two linear regulator controllers on a single IC to provide control and protection for three voltages. The LM2638 includes a built-in charge pump that eliminates the need for a similar external device.
A charge pump oscillator pin replaces the LM2637’s overvoltage protection pin, while maximum PWM duty cycle is increased from 95 percent to 100 percent to reduce loading to the charge pump during standby mode.Both devices offer two user-selectable overcurrent protection modes: one is designed to maximize accuracy, while the other is intended to minimize cost. The ICs’ switching section is designed to supply the MPU core or other high-current loads with a programmable voltage from 3.3V to 1.3V. Operating frequency can be adjusted between 50kHz and 1MHz through an external resistor.
The controllers are designed to generate the necessary voltages for the GTL+ bus, clock, graphics core, AGP interface, memory, or any other medium-to-low-current loads. Additional features include a 5-bit programmable DAC with a typical tolerance of 1 percent, overvoltage protection and undervoltage latch off, a logic-controlled output enable and a power-good signal that indicates when the output voltage is within a specified range.Available in National’s 24-pin SOIC, the LM2637M and LM2638M are priced at $1.50 each in quantities of 1,000.