Features: ` 4.5V to 30V input range
` Adjustable output (1.5V to 7V)
` 200 kHz to 400 kHz adjustable operating frequency
` Externally synchronizable
` On-board power good function
` Precision 1.24V reference output
` 0.8 mA typical quiescent current
` 0.1 A shutdown current
` Thermal shutdown
` Direct current limit protection
` Input undervoltage lockout
` Output undervoltage shutdown protection
` Output overvoltage shutdown protection
` Programmable soft-start function
` Tiny TSSOP packageApplication· Notebook and subnotebook computers
· Cellular phones
· Portable instruments
· Battery-powered digital devicesSpecificationsIf Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
Voltages from the indicated
pins to GND and PGND:
VIN ............................................................−0.3V to 32V
CBOOT ......................................................−0.3V to 37V
SD .............................................................−0.3V to 32V
SW ............................................................−0.3V to 32V
CSH, CSL .....................................................−0.3V to 8V
FPWM, SYNC ..............................................−0.3V to 10V
Power Dissipation (TA =70°C), (Note 2) .......... 720mW
Storage Temperature Range........... −65°C to +150°C
Soldering Dwell Time,Temperature (Note 3)
Wave 4 sec, .......................................................260°C
Infrared 10 sec, ..................................................240°C
Vapor Phase 75 sec, ...........................................219°C
ESD Rating (Note 4) ..............................................1.5 kV
DescriptionThe 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 kHz and 400 kHz. An external shutdown pin can be used to disable the device and reduce the quiescent current to 0.1 A. 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 come up in the preset time.
LM2631 Data Sheet
