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PDF LM3200 Data sheet ( Hoja de datos )
| Número de pieza | LM3200 | |
| Descripción | Step-Down DC-DC Converter with Bypass Mode for RF Power Amplifiers | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM3200 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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November 2004
LM3200
Miniature, Adjustable, Step-Down DC-DC Converter with
Bypass Mode for RF Power Amplifiers
General Description
The LM3200 is a DC-DC converter optimized for powering
RF power amplifiers (PAs) from a single Lithium-Ion cell. It
steps down an input voltage of 2.7V to 5.5V to a variable
output voltage of 0.8V to 3.6V. The output voltage is set
using an analog input ( VCON) for optimizing efficiency of the
RF PA at various power levels.
The LM3200 offers superior features and performance for
mobile phones and similar RF PA applications. Fixed-
frequency PWM mode minimizes RF interference. Bypass
mode turns on an internal bypass switch to power the PA
directly from the battery. LM3200 has both forced and auto-
matic bypass modes. Shutdown mode turns the device off
and reduces battery consumption to 0.1 µA (typ.). The
LM3200 is available in a 10-pin lead free micro SMD pack-
age. A high switching frequency (2 MHz) allows use of tiny
surface-mount components. Only three small external
surface-mount components, an inductor and two ceramic
capacitors are required.
Features
n 2 MHz (typ.) PWM Switching Frequency
n Operates from a single Li-Ion cell (2.7V to 5.5V)
n Variable Output Voltage (0.8V to 3.6V)
n 300 mA Maximum load capability (PWM mode)
n 500 mA Maximum load capability (Bypass mode)
n PWM, Forced and Automatic Bypass Mode
n High Efficiency (96% Typ at 3.6VIN, 3.2VOUT at 120 mA)
from internal synchronous rectification
n 10-pin micro SMD Package
n Current Overload Protection
n Thermal Overload Protection
Applications
n Cellular Phones
n Hand-Held Radios
n RF PC Cards
n Battery Powered RF Devices
Typical Application
20126101
© 2004 National Semiconductor Corporation DS201261
www.national.com
1 page  
Typical Performance Characteristics (Circuit in Figure 1, PVIN = VDD = EN = 3.6V, BYP = 0V, TA =
25˚C, unless otherwise noted)
Quiescent Supply Current vs Supply Voltage
Shutdown Supply Current vs Temperature
(EN = 0V)
20126104
Switching Frequency Variation vs Temperature
(VOUT = 1.5V, IOUT = 200 mA)
20126105
Output Voltage vs Supply Voltage
(VOUT = 1.5V)
20126106
Output Voltage vs Temperature
(VOUT = 1.5V)
20126107
Output Voltage vs Temperature
(VOUT = 3.25V)
20126108
5
20126109
www.national.com
5 Page 
Operation Description (Continued)
sophisticated portable device with complex power manage-
ment needs. Fixed-frequency PWM operation offers regu-
lated output at high efficiency while minimizing interference
with sensitive IF and data acquisition circuits. Bypass mode
(Forced or Automatic) turns on an internal FET bypass
switch to power the PA directly from the battery. Shutdown
mode turns the device off and reduces battery consumption
to 0.1 µA (typ).
DC PWM mode output voltage precision is +/-2% for
3.6VOUT. Efficiency is typically around 96% for a 120 mA
load with 3.2V output, 3.6V input. PWM mode quiescent
current is 0.7 mA typ. 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 resis-
tors. This ensures longer battery life by being able to change
the PA supply voltage dynamically depending on its trans-
mitting power.
Additional features include current overload protection, over
voltage protection and thermal shutdown.
The LM3200 is constructed using a chip-scale 10-pin micro
SMD package. This package offers the smallest possible
size, 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 few exter-
nal components are required for implementation. Use of a
micro SMD package requires special design considerations
for implementation. (See Micro SMD Package Assembly and
use in the Applications Information section.) Its fine bump-
pitch 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 con-
troller should set EN low during power-up and other low
supply voltage conditions. (See Shutdown Mode in the De-
vice Information section.)
FIGURE 1. Typical Operating System Circuit
20126136
Circuit Operation
Referring to Figure 1, the LM3200 operates as follows. Dur-
ing the first part of each switching cycle, the control block in
the LM3200 turns on the internal PFET (P-channel MOS-
FET) switch. This allows current to flow from the input
through the inductor to the output filter capacitor and load.
The inductor limits the current to a ramp with a slope of
around (VIN-VOUT)/L, by storing energy in a magnetic field.
During the second part of each cycle, the controller turns the
PFET switch off, blocking current flow from the input, and
then turns the NFET (N-channel MOSFET) synchronous
rectifier on. In response, the inductor’s magnetic field col-
lapses, generating a voltage that forces current from ground
through the synchronous rectifier to the output filter capacitor
and load. As the stored energy is transferred back into the
circuit and depleted, the inductor current ramps down with a
slope around VOUT/L. The output filter capacitor stores
charge when the inductor current is going high, and releases
it when inductor current is going low, smoothing the voltage
across the load.
The output voltage is regulated by modulating the PFET
switch on time to control the average current sent to the load.
The effect is identical to sending a duty-cycle modulated
rectangular wave formed by the switch and synchronous
rectifier at SW to a low-pass filter formed by the inductor and
output filter capacitor. The output voltage is equal to the
average voltage at the SW pin.
PWM Mode
While in PWM (Pulse Width Modulation) mode, the output
voltage is regulated by switching at a constant frequency
and then modulating the energy per cycle to control power to
the load. Energy per cycle is set by modulating the PFET
switch on-time pulse width to control the peak inductor cur-
rent. This is done by comparing the signal from the PFET
drain current to a slope-compensated reference current gen-
erated by the error amplifier. At the beginning of each cycle,
the clock turns on the PFET switch, causing the inductor
current to ramp up. When the current sense signal ramps
past the error amplifier signal, the PWM comparator turns off
the PFET switch and turns on the NFET synchronous recti-
fier, ending the first part of the cycle. If an increase in load
pulls the output down, the error amplifier output increases,
which allows the inductor current to ramp higher before the
comparator turns off the PFET. This increases the average
current sent to the output and adjusts for the increase in the
load. Before appearing at the PWM comparator, a slope
11 www.national.com
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet LM3200.PDF ] | |
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