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PDF LM2631 Data sheet ( Hoja de datos )
| Número de pieza | LM2631 | |
| Descripción | Synchronous Step-Down Power Supply Controller | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM2631 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
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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 con-
verters provide core CPU power in battery-operated sys-
tems.
High efficiency is achieved by using synchronous rectifica-
tion and pulse-skipping mode operation at light load. Inex-
pensive 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 regula-
tion 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 µA. In low
noise applications, bringing the FPWM pin high can force the
device to operate in constant frequency mode. Other fea-
tures 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.
Features
n 4.5V to 30V input range
n Adjustable output (1.5V to 7V)
n 200 kHz to 400 kHz adjustable operating frequency
n Externally synchronizable
n On-board power good function
n Precision 1.24V reference output
n 0.8 mA typical quiescent current
n 0.1 µA shutdown current
n Thermal shutdown
n Direct current limit protection
n Input undervoltage lockout
n Output undervoltage shutdown protection
n Output overvoltage shutdown protection
n Programmable soft-start function
n Tiny TSSOP package
Applications
n Notebook and subnotebook computers
n Cellular phones
n Portable instruments
n Battery-powered digital devices
Typical Application Circuit
© 1999 National Semiconductor Corporation DS100937
DS100937-1
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Quiscent Supply Current vs Supply Voltage
(Not Switching, FPWM = Low, VOUT = 2.0V)
Quiscent Supply Current vs Supply Voltage
(FPWM = Low, VOUT = 3.3V)
DS100937-15
Supply Current vs Oscillator Frequency
(FPWM = High)
DS100937-16
Oscillator Frequency vs Adjusting Resistor
DS100937-17
Oscillator Frequency vs Junction Temperature
DS100937-18
Reference Voltage vs Junction Temperature
DS100937-13
5
DS100937-14
www.national.com
5 Page 
Application Circuits (Continued)
FIGURE 3. High Efficiency, 300 kHz, 5V to 2.5V Converter.
Efficiency is 94% (typ) at 1A load.
DS100937-5
11 www.national.com
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LM2631.PDF ] | |
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