LM2635 5-Bit Programmable Synchronous Buck Regulator Controller
May 2000
LM2635 5-Bit Programmable Synchronous Buck Re...
LM2635 5-Bit Programmable Synchronous Buck Regulator Controller
May 2000
LM2635 5-Bit Programmable Synchronous Buck Regulator Controller
General Description
The LM2635 is a high speed controller designed specifically for use in synchronous DC/DC buck converters for the Pentiumâ„¢ 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 rDS_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. 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 t...