Block Diagram

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Operation Description

The LM3203 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 500mA. Maximum load range may vary from

this depending on input voltage, output voltage and the

inductor chosen.

The device has all three of the 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 interfer-

ence with sensitive IF and data acquisition circuits. Bypass

mode turns on an internal FET bypass switch to power the

PA directly from the battery. This helps the RF power ampli-

fier maintain its operating power during low battery condi-

tions by reducing the dropout voltage across the LM3203.

Shutdown mode turns the device off and reduces battery

consumption to 0.1µA (typ.).

DC PWM mode output voltage precision is +/-2% for

1.2V

with 3.2V output, 3.6V input. PWM mode quiescent current is

0.675 mA (typ.). The FB pin voltage is dynamically program-

mable from 0.267V to 1.2V by adjusting the voltage on the

V

External divider resistors can change the output

voltge range. 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 LM3203 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. Use of a micro SMD package requires

special design considerations for implementation. (See Mi-

cro 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 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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