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PDF LM3355 Data sheet ( Hoja de datos )
| Número de pieza | LM3355 | |
| Descripción | -05 to 5.6 V regulated 50mA buck-boost switched capacitor DC/DC converter For white LED display backlights | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM3355 (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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December 2001
LM3355
Regulated 50mA Buck-Boost Switched Capacitor DC/DC
Converter
General Description
The LM3355 is a CMOS switched capacitor DC/DC con-
verter that produces a regulated output voltage by automati-
cally stepping up (boost) or stepping down (buck) the input
voltage. It accepts an input voltage between 2.5V and 5.5V.
The LM3355 is available with a standard output voltage of
4.1V (ideal for white LED applications). If other output volt-
age options between 1.8V and 4.1V are desired for other
applications, please contact your National Semiconductor
representative.
The LM3355’s proprietary buck-boost architecture enables
up to 50 mA of load current at an average efficiency greater
than 75%. Typical operating current is only 375 µA and the
typical shutdown current is only 2.3 µA.
The LM3355 is available in a 10-pin MSOP package. This
package has a maximum height of only 1.1 mm.
The high efficiency of the LM3355, low operating and shut-
down currents, small package size, and the small size of the
overall solution make this device ideal for battery powered,
portable, and hand-held applications.
See the LM3352 for up to 200mA of output current.
Features
n Regulated VOUT with ±3% accuracy
n Standard output voltage of 4.1V
n Custom output voltages available from 1.8V to 4.1V in
100 mV increments
n 2.5V to 5.5V input voltage
n Up to 50 mA output current
n >75% average efficiency
n Uses few, low-cost external components
n Very small solution size
n 375 µA typical operating current
n 2.3 µA typical shutdown current
n 1 MHz switching frequency (typical)
n Architecture and control methods provide high load
current and good efficiency
n MSOP-10 package
n Over-temperature protection
Applications
n White LED display backlights
n 1-cell Lilon battery-operated equipment including PDAs,
hand-held PCs, cellular phones
n Flat panel displays
n Hand-held instruments
n NiCd, NiMH, or alkaline battery powered systems
Typical Operating Circuit
© 2001 National Semiconductor Corporation DS200219
DS200219-1
www.national.com
1 page  
Typical Performance Characteristics Unless otherwise specified TA = 25˚C. (Continued)
Maximum VOUT Ripple vs. COUT
Maximum VOUT Ripple vs. COUT
DS200219-32
Applications Information
DS200219-30
FIGURE 1. Block Diagram
DS200219-3
Operating Principle
The LM3355 is designed to provide a step-up/step-down
voltage regulation in battery powered systems. It combines
switched capacitor circuitry, reference, comparator, and
shutdown logic in a single 10-pin MSOP package. The
LM3355 can provide a regulated voltage between 1.8V and
4.1V from an input voltage between 2.5V and 5.5V. It can
supply a load current up to 50 mA.
As shown in Figure 1, the LM3355 employs two feedback
loops to provide regulation in the most efficient manner
possible. The first loop is from VOUT through the comparator
COMP, the AND gate G1, the phase generator, and the
switch array. The comparator’s output is high when VOUT is
less than the reference VREF. Regulation is provided by
gating the clock to the switch array. In this manner, charge is
transferred to the output only when needed. The second
loop controls the gain configuration of the switch array. This
loop consists of the comparator, the digital control block, the
phase generator, and the switch array. The digital control
block computes the most efficient gain from a set of five
gains based on inputs from the A/D and the comparator. The
gain signal is sent to the phase generator which then sends
the appropriate timing and configuration signals to the switch
array. This dual loop provides regulation over a wide range of
loads efficiently.
Since efficiency is automatically optimized, the curves for
VOUT vs. VIN and Efficiency vs. VIN in the Typical Perfor-
mance Characteristics section exhibit small variations. The
reason is that as input voltage or output load changes, the
digital control loops are making decisions on how to optimize
efficiency. As the switch array is reconfigured, small varia-
tions in output voltage and efficiency result. In all cases
where these small variations are observed, the part is oper-
ating correctly; minimizing output voltage changes and opti-
mizing efficiency.
Charge Pump Capacitor Selection
A 0.33 µF ceramic capacitor is suggested for C1 and C2. To
ensure proper operation over temperature variations, an
X7R dielectric material is recommended.
5 www.national.com
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| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet LM3355.PDF ] | |
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