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LM2635 ,Synchronous Buck Regulator ControllerPin Descriptionsabled when this pin is pulled low. It is internally pulled up toV via a 90 μA curre ..
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LM2631MTC-ADJ-LM2631MTCX-ADJ
Synchronous Step-Down Voltage Regulator [Not recommended for new designs]
LM2631
Synchronous Step-Down Power Supply Controller
General DescriptionThe LM2631 controller providesallthe active functionsfor
step-down (buck) switching converters. These dc-to-dc con-
verters provide core CPU powerin battery-operated sys-
tems.
High efficiencyis achievedby using synchronous rectifica-
tionand pulse-skipping mode operationat light load. Inex-
pensive N-channel MOSFETsare usedto reduce system
cost. Bootstrap circuitis usedto drive the high-side
N-channel MOSFET.
Currentmode controlschemeis usedto improve lineregula-
tion and transient response, also provides cycle-by-cycle
current limiting.
The operating frequencyis adjustable between 200kHzand
400 kHz.An external shutdownpincanbe usedto disable
the deviceand reducethe quiescentcurrent to0.1μA.Inlow
noise applications,bringing theFPWMpinhighcan forcethe
deviceto operatein constant frequency mode. Other fea-
tures includethe external synchronization pin, andthe
PGOODpinto indicatethe stateofthe output voltage.
Protection circuitry includes thermal shutdown, undervoltage
and overvoltage shutdown protection, soft-start capability,
andtwo levelsof current limits:Thefirst level simply limits
the load current directly;atthe second level,ifthe load pulls
the output voltage down below 80%ofthe regulated value,
the chipwill shut down. This operationis disabled during
startup,butan internal timerwill enableitifthe output does
not comeupinthe preset time.
Features 4.5Vto 30V input range Adjustable output (1.5Vto7V) 200 kHzto400kHz adjustable operating frequency Externally synchronizable On-board power good function Precision 1.24V reference output0.8mA typical quiescent current0.1μA 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 package
Applications Notebookand subnotebook computers Cellular phones Portable instruments Battery-powered digital devices
Typical Application CircuitDS100937-1
April 1999
LM2631
Synchronous
Step-Down
Power
Supply
Controller 1999 National Semiconductor Corporation DS100937
