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PDF LM3218 Data sheet ( Hoja de datos )
| Número de pieza | LM3218 | |
| Descripción | Step-Down DC-DC Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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January 21, 2009
LM3218
650 mA Miniature, Adjustable, Step-Down DC-DC
Converter for RF Power Amplifiers
General Description
The LM3218 is a DC-DC converter with inductor which is op-
timized for powering RF power amplifiers (PAs) from a single
Lithium-Ion cell. It steps down an input voltage in the range
from 2.7V to 5.5V to an adjustable output voltage of 0.8V to
3.6V. Output voltage is set by using a VCON analog input to
control power levels and efficiency of the RF PA.
The LM3218 offers superior electrical performance for mobile
phones and similar RF PA applications with a reduced foot-
print (3mm x 2.5mm x 1.2mm). Fixed-frequency PWM oper-
ation minimizes RF interference. A shutdown function turns
the device off and reduces battery consumption to 0.01 µA
(typ.).
The LM3218 is available in an integrated inductor 8–pin LTCC
package. A high switching frequency (2 MHz typ.) allows use
of tiny surface-mount components. Only two small external
surface-mount components, two ceramic capacitors, are re-
quired. The overall board space is reduced up to 25% from
the typical discrete inductor solution.
Features
■ Includes 2.6 µH Inductor in very small form factor (3mm x
2.5mm x 1.2mm)
■ 2 MHz (typ.) PWM Switching Frequency
■ Operates from a single Li-Ion cell (2.7V to 5.5V)
■ Adjustable Output Voltage (0.8V to 3.6V)
■ Fast Output Voltage Transient (0.8V to 3.4V in 25 µs typ.)
■ 650 mA Maximum load capability
■ High Efficiency (95% typ. at 3.9 VIN, 3.4 VOUT at 400 mA)
■ 8-pin LTCC Package
■ Current Overload Protection
■ Thermal Overload Protection
Applications
■ Cellular Phones
■ Hand-Held Radios
■ RF PC Cards
■ Battery-Powered RF Devices
Typical Application
FIGURE 1. LM3218 Typical Application
30050401
© 2009 National Semiconductor Corporation 300504
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1 page  
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation
of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions,
see the Electrical Characteristics tables.
Note 2: All voltages are with respect to the potential at the GND pins. The LM3218 is designed for mobile phone applications where turn-on after power-up is
controlled by the system controller and where requirements for a small package size overrule increased die size for internal Under Voltage Lock-Out (UVLO)
circuitry. Thus, it should be kept in shutdown by holding the EN pin low until the input voltage exceeds 2.7V.
Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ
= 125°C (typ.).
Note 4: The Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. (MIL-STD-883 3015.7) The machine model is a 200
pF capacitor discharged directly into each pin.
Note 5: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be de-
rated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125°C), the maximum power dissipation
of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the following
equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Note 6: Junction-to-ambient thermal resistance (θJA) is taken from thermal measurements, performed under the conditions and guidelines set forth in the JEDEC
standard JESD51-7. A 4–layer, 4" x 4", 2/1/1/2 oz. Cu board as per JEDEC standards is used for the measurements.
Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Due to the pulsed nature of the testing TA = TJ for the electrical characteristics table.
Note 8: The parameters in the electrical characteristics table are tested under open loop conditions at PVIN = VDD = 3.6V unless otherwise specified. For
performance over the input voltage range and closed-loop results, refer to the datasheet curves.
Note 9: Shutdown current includes leakage current of PFET.
Note 10: IQ specified here is when the part is not switching. For operating quiescent current at no load, refer to datasheet curves.
Note 11: Current limit is built-in, fixed, and not adjustable. Electrical Characteristic table reflects open loop data (FB = 0V and current drawn from SW pin ramped
up until cycle by cycle limit is activated). Refer to System Characteristics table for maximum output current.
Note 12: Ripple voltage should be measured at COUT electrode on a well-designed PC board and using the suggested inductor and capacitors.
Note 13: National Semiconductor recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper ESD handling
procedures can result in damage.
Note 14: Linearity limits are ±3% or ±50 mV whichever is larger.
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5 www.national.com
5 Page 
Block Diagram
FIGURE 2. Functional Block Diagram
30050404
Operation Description
The LM3218 is a simple, step-down DC-DC converter with a
2.6 µH series inductor substrate optimized for powering RF
power amplifiers (PAs) in mobile phones, portable communi-
cators, and similar battery powered RF devices. It is designed
to allow the RF PA to operate at maximum efficiency over a
wide range of power levels from a single Li-Ion battery cell. It
is based on current mode buck architecture, with syn-
chronous rectification for high efficiency. It is designed for a
maximum load capability of 650 mA when VOUT > 1.05V (typ.)
and 400 mA when VOUT < 1.00V (typ.) in PWM mode.
Maximum load range may vary from this depending on input
voltage, output voltage and the inductor chosen.
Efficiency is typically around 95% for a 400 mA load with 3.4V
output, 3.9V input. The LM3218 has an RDSON management
scheme to increase efficiency when VOUT ≤ 1V. The output
voltage is dynamically programmable from 0.8V to 3.6V by
adjusting the voltage on the control pin without the need for
external feedback resistors. This prolongs battery life by
changing the PA supply voltage dynamically depending on its
transmitting power.
Additional features include current overload protection and
thermal overload shutdown.
The LM3218 is constructed using a chip-scale 8-pin micro
SMD package and a LTCC inductor substrate. This package
offers the smallest possible integrated solution footprint for
space-critical applications such as cell phones, where board
area is an important design consideration. Use of a high
switching frequency (2 MHz) reduces the size of external
components. As shown in Figure 1, only two external capac-
itors are required for implementation. Use of this module
requires special design considerations for implementation.
(See LTCC Module Package Assembly and Use in the Appli-
cations Information section). The board mounting requires
careful board design and precision assembly equipment. Use
of this package is best suited for opaque-case applications,
where its edges are not subject to high-intensity ambient red
or infrared light. Also, the system controller should set EN low
during power-up and other low supply voltage conditions.
(See Shutdown Mode in the Device Information section.)
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM3218.PDF ] | |
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