LM3204 Datasheet, PDF (11/16 Pages) National Semiconductor (TI) – Miniature, Adjustable, Step-Down DC-DC Converter with Bypass Mode for RF Power Amplifiers

Block Diagram
Operation Description
The LM3204 is a simple, step-down DC-DC converter with a
bypass switch, optimized for powering RF power amplifiers
(PAs) in mobile phones, portable communicators, 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 synchronous rectifica-
tion for high efficiency. It is designed for a maximum load
capability of 300mA in PWM mode and 500mA in bypass
mode. Maximum load range may vary from this depending
on input voltage, output voltage and the inductor chosen.
The device has all three of pin-selectable operating modes
required for powering RF PAs in mobile phones and other
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. This helps
the RF power amplifier maintain its operating power during
low battery conditions by reducing the dropout voltage
across the LM3204. Shutdown mode turns the device off and
reduces battery consumption to 0.1µA (typ.).
DC PWM mode output voltage precision is +/-2% for
3.6V_OUT. Efficiency is typically around 96% for a 120mA load
20138935
with 3.2V output, 3.6V input. PWM mode quiescent current is
0.72mA typ. The output voltage is dynamically program-
mable from 0.8V to 3.6V by adjusting the voltage on the
control pin (V_CON) without the need for external feedback
resistors. This ensures longer battery life by being able to
change the PA supply voltage dynamically depending on its
transmitting power.
Additional features include current overload protection, over
voltage protection and thermal shutdown.
The LM3204 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 (2MHz typ.) 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.)
11
www.national.com