LM2631 Datasheet | National Semiconductor

LM2631 Synchronous Step-Down Power Supply Controller April 1999 LM2631 Synchronous Step-Down Power Supply Controller General Description The LM2631 controller provides all the active functions for step-down (buck) switching converters. These dc-to-dc converters provide core CPU power in battery-operated systems. High efficiency is achieved by using synchronous rectification and pulse-skipping mode operation at light load. Inexpensive N-channel MOSFETs are used to reduce system cost. Bootstrap circuit is used to drive the high-side N-channel MOSFET. Current mode control scheme is used to improve line regulation and transient response, also provides cycle-by-cycle current limiting. The operating frequency is adjustable between 200 k Hz and 400 k Hz. An external shutdown pin can be used to disable the device and reduce the quiescent current to 0.1 µA. In low noise applications, bringing the FPWM pin high can force the device to operate in constant frequency mode. Other Features include the external synchronization pin, and the PGOOD pin to indicate the state of the output voltage. Protection circuitry includes thermal shutdown, undervoltage and overvoltage shutdown protection, soft-start capability, and two levels of current limits: The first level simply limits the load current directly; at the second level, if the load pulls the output voltage down below 80% of the regulated value, the chip will shut down. This operation is disabled during startup, but an internal timer will enable it if the output does not e up in the preset time. Features n n n n n n n n n n n n n n n 4.5V to 30V input range Adjustable output (1.5V to 7V) 200 k Hz to 400 k Hz adjustable operating frequency Externally synchronizable On-board power good function Precision 1.24V reference output 0.8 m A typical quiescent current 0.1 µA shutdown current Thermal shutdown Direct current limit protection Input undervoltage lockout Output undervoltage shutdown protection Output overvoltage shutdown...