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PDF LM2611AMFX Data sheet ( Hoja de datos )
| Número de pieza | LM2611AMFX | |
| Descripción | 1.4MHz Cuk Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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January 2002
LM2611
1.4MHz Cuk Converter
General Description
The LM2611 is a current mode, PWM inverting switching
regulator. Operating from a 2.7 - 14V supply, it is capable of
producing a regulated negative output voltage of up to
−(36-VIN(MAX)). The LM2611 utilizes an input and output
inductor, which enables low voltage ripple and RMS current
on both the input and the output. With a switching frequency
of 1.4MHz, the inductors and output capacitor can be physi-
cally small and low cost. High efficiency is achieved through
the use of a low RDS(ON) FET.
The LM2611 features a shutdown pin, which can be acti-
vated when the part is not needed to lower the Iq and save
battery life. A negative feedback (NFB) pin provides a simple
method of setting the output voltage, using just two resistors.
Cycle-by-cycle current limiting and internal compensation
further simplify the use of the LM2611.
The LM2611 is available is a small SOT23-5 package. It
comes in two grades:
Current Limit
RDS(ON)
Grade A
1.2A
0.5Ω
Grade B
0.9A
0.7Ω
Features
n 1.4MHz switching frequency
n Low RDS(ON) DMOS FET
n 1mVp-p output ripple
n −5V at 300mA from 5V input
n Better regulation than a charge pump
n Uses tiny capacitors and inductors
n Wide input range: 2.7V to 14V
n Low shutdown current: <1uA
n 5-lead SOT-23 package
Applications
n MR Head Bias
n Digital camera CCD bias
n LCD bias
n GaAs FET bias
n Positive to negative conversion
Typical Application Circuit
© 2002 National Semiconductor Corporation DS200181
20018117
www.national.com
1 page  
Typical Performance Characteristics (Continued)
VNFB vs VIN
TA = 25˚C, VOUT = −5V
VNFB vs Ambient Temperature
VIN = 5V
INFB vs VIN
TA = 25˚C, VOUT = −5V
20018107
20018124
INFB vs Ambient Temperature
VIN = 3.5V, VOUT = −5V
20018108
Iq vs Ambient Temperature (No Load)
20018109
VSHUTDOWN vs Ambient Temperature
VIN = 5V
20018144
5
20018110
www.national.com
5 Page 
Application Circuits (Continued)
Shutdown/Soft Start
A soft start circuit is used in switching power supplies to limit
the input inrush current upon start-up. Without a soft-start
circuit, the inrush current can be several times the
steady-state load current, and thus apply unnecessary
stress to the input source. The LM2611 does not have
soft-start circuitry, but implementing the circuit in Figure 11
will lower the peak inrush current. The SHDN pin is coupled
to the output through CSS. The LM2611 is toggled between
shutdown and run states while the output slowly decreases
to its steady-state value. The energy required to reach
steady-state is spread over a longer time and the input
current spikes decrease (see Figure 12 and Figure 13).
FIGURE 11. LM2611 Soft Start Circuit
20018125
20018142
FIGURE 12. Start-Up Waveforms with Soft Start Circuit
20018141
FIGURE 13. Start-Up Waveforms without Soft Start
Circuit
11 www.national.com
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet LM2611AMFX.PDF ] | |
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