LM3204 datasheet(11/16 Pages) NSC

11 / 16 page

Block Diagram

20138935

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

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.)

LM3204 Datasheet(PDF) 11 Page - National Semiconductor (TI)

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