SYSTEM

CONTROLLER

LM3204

2.7V to 5.5V

0.8V to 3.6V

L1

2.2 PH

C4**

0.1 PF

*Place C1 close to PVIN.

**Place C4 close to VDD.

C2

4.7 PF

SW

FB

EN

PGND

SGND

DAC

BYP

BYPOUT

ON/OFF

C1*

10 PF

LM3204

www.ti.com

SNVS351C – JUNE 2005 – REVISED APRIL 2013

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 rectification 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 management needs. Fixed-frequency PWM operation

offers regulated 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.).

load with 3.2V output, 3.6V input. PWM mode quiescent current is 0.72mA typ. The output voltage is dynamically

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 DSBGA 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 34, only few external components are required for implementation. Use of a DSBGA package requires

special design considerations for implementation. (See DSBGA Package Assembly 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

controller should set EN low during power-up and other low supply voltage conditions. (See Shutdown Mode

section.)

Figure 34. Typical Operating System Circuit

Circuit Operation

Referring to Figure 34, the LM3204 operates as follows. During the first part of each switching cycle, the control

block in the LM3204 turns on the internal PFET (P-channel MOSFET) 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

controller turns the PFET switch off, blocking current flow from the input, and then turns the NFET (N-channel

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