LM2635 Datasheet | National Semiconductor

Description 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 parators are built in to monitor the output voltage and override the primary control loop when necessary. The PWM frequency is adjustable from 50 k Hz 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. Bi CMOS 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 acmodate 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. Features n n n n n n n n n n n 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 k Hz to 1 MHz Dynamic output voltage positioning...