LM2635  Product Folder

The LM2635 is a high speed controller designed specifically for use in synchronous DC/DC buck converters for the Pentium™ II or Deschutes microprocessor. A 5-bit DAC accepts the VID code directly from the CPU and adjusts the output voltage from 1.8V to 3.5V. It provides the power good, over-voltage protection, and output enable features as required by Intel VRM specifications. Current limiting is achieved by monitoring the voltage drop across the r_{DS_ON} of the high side MOSFET, which eliminates an expensive current sense resistor.

The LM2635 employs a fixed-frequency voltage mode PWM architecture. To provide a faster response to a large and fast load transient, two ultra-fast comparators are built in to monitor the output voltage and override the primary control loop when necessary. The PWM frequency is adjustable from 50 kHz to 1 MHz through an external resistor. The wide range of PWM frequency gives the power supply designer the flexibility to make trade-offs between load transient response performance, MOSFET cost and the overall efficiency. The adaptive non-overlapping MOSFET gate drivers help avoid any potential shoot-through problem while maintaining high efficiency. BiCMOS gate drivers with rail-to-rail swing ensure that no spurious turn-on occur. When only 5V is available, a bootstrap structure can be employed to accommodate an NMOS high side switch. The precision reference trimmed to 2% over temperature is available externally for use by other regulators. Dynamic positioning of load voltage, which helps cut the number of output capacitors, can also be implemented easily.

• 1.8V to 3.5V 5-bit programmable output voltage
• Synchronous rectification
• Power Good flag and output enable
• Over-voltage protection
• Initial Output Accuracy: 2% over temperature
• Current limit without external sense resistor
• Adaptive non-overlapping MOSFET gate drives
• Adjustable switching frequency: 50 kHz to 1 MHz
• Dynamic output voltage positioning
• 1.256V reference voltage available externally
• Plastic SO-20 package

• Motherboard power supply/VRM for Cyrix Gxm, Cyrix Gxi, Cyrix MII, Pentium™ II, Deschutes, Pentium Pro, 6x86 and K6 processors
• 5V to 1.8V-3.5V high current power supplies