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PDF LM2630MTC-ADJ Data sheet ( Hoja de datos )
| Número de pieza | LM2630MTC-ADJ | |
| Descripción | Synchronous Step-Down Power Supply Controller | |
| Fabricantes | National Semiconductor | |
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February 1999
LM2630
Synchronous Step-Down Power Supply Controller
General Description
The LM2630 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
shut down, soft-start capability, and two levels of current lim-
its: 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 willshut down. This
latched operation is disabled during startup, but an internal
timer will enable it if the output does not come up in the pre-
set time.
Features
n 4.5V to 30V input range
n Adjustable output (1.8V to 6V)
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 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 DS100120
DS100120-1
www.national.com
1 page  
Typical Performance Characteristics
Efficiency vs Load Current
(FPWM = Low, VOUT = 3.3V)
Efficiency (FPWM = High, Input Voltage = 16V,
VOUT= 2.9V)
DS100120-11
Quiscent Supply Current vs Supply Voltage
(Not Switching, FPWM = Low, VOUT = 2.0V)
DS100120-12
Quiscent Supply Current vs Supply Voltage
(FPWM = Low, VOUT = 3.3V)
DS100120-15
Supply Current vs Oscillator Frequency
(FPWM = High)
DS100120-16
Oscillator Frequency vs Adjusting Resistor
DS100120-17
5
DS100120-18
www.national.com
5 Page 
Design Procedure (Continued)
FIGURE 2. The Typical 2.5V Application Circuit
DS100120-4
TABLE 1. Components for Typical 2.5V, 300kHz Application Circuits
Input Voltage
Output Current
Application
Q1 and Q2
Inductor L1
Input Capacitors
Output Capacitors
Rectifier D1
Sensing Resistor R3
Compensation components C8 and
R8
4.75V to 24V
4A
Notebook
Fairchild FDS6680; Siliconix
Si4410DY; or International Rectifier
IRF7805
Sumida CDRH127-7R6: 7.6µH, 5.9A
2 x 22µF, 35V Sprague 593D or TPS
2 x 220µF, 10V Sprague 593D or TPS
Motorola MBRS140T3
15 mΩ IRC
R8 = 3.3 KΩ, C8 = 1 nF
4.5V to 6V
10A
Desktop
Fairchild FDB7030L; or Motorola
MTB75N03HDL
Pulse PE-53681: 2.5 µH, 11.4A
2 x 220 µF, 10V Sanyo OS-CON SA
3 x 330 µF, 6.3V Sanyo OS-CON SA
Motorola MBRS340T3
3 x 20 mΩ IRC
R8 = 4 KΩ, C8 = 1nF
When the input voltage is low (less than 5V), the bootstrap
function cannot deliver enough gate voltage to fully drive the
high-side MOSFET on, which increases Rdson, and conse-
quently reduces efficiency. An external charge-pump doubler
can be added to double the CBOOT pin voltage (see Figure
3). It can also be added to the VIN pin to increase the gate
drive voltage at both high-side and low-side MOSFETs.
11 www.national.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LM2630MTC-ADJ.PDF ] | |
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