LINEAR LTM8025 User Guide

L DESIGN IDEAS

Self-Contained 3A µModule Buck Regulator Produces 0.8V–24V Output

from 3.6V–36V Input by David Ng

AUX PGOOD

Introduction Easy Layout

GND GND

RT RADJ

Ask any group of engineers, “What The LTM8025’s high level of integration would you do with a 3A DC/DC con- simplifies the design of just about any verter?” and you will probably get a 3A power supply. Just add two resis-

wide range of answers—from powering SHDN tors, input and output capacitance to

VOUT BIAS

a DSP rail at 1.8V to running a bank make a complete power supply. Layout

of 24V switching I/O. Typically, these is easy, as shown in Figure 1. Figures two particular applications would 2 and 3 show the schematic and ef- require completely different DC/DC ficiency of the LTM8025 producing

controller ICs and topologies. How- CINCOUT 12V bus power from a 24V source,

ever, the LTM8025 µModule DC/DC while Figure 4 shows the LTM8025

converter can satisfy the requirements GND producing 1.8V from an input range

of these and just about any other 3A THERMAL VIAS TO GND of 3.6V to 36V.

applications. Figure 1. Layout is easy with the LTM8025.

The LTM8025 3A µModule DC/DC Versatile Feature Set

buck converter operates from 3.6V to The LTM8025 integrates the con- The LTM8025 may be operated over 36V inputs to produce output voltages troller, control circuitry, inductor, a wide frequency, from 200k Hz to as low as 0.8V and as high as 24V. power switch and rectifier all into a 2.4MHz, and may be synchronized to Furthermore, the LTM8025 features single IC form factor 15mm × 9mm × an external clock source through the single cycle Burst Mode® operation, 4.32mm package. This LGA package is SYNC pin. The LTM8025 start-up is

EF FI CI EN CY

so it is able to handle a wide range Ro HS (e3) compliant, and features gold controlled through its RUN/SS pin, of load currents, from no load to 3A, pads for easy assembly in both leaded which also serves to put the part into with minimum ripple. and unleaded solder processes. continued on page 42

VIN = 24V

VIN* VOUT

VIN VOUT

22V TO 36V 12V AT 3A

RUN/SS AUX

LTM8025 BIAS SHARE PGOOD

RT ADJ SYNC GND

*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS

Figure 2. A complete 12V at 3A power supply requires

OUTPUT CURRENT (m A)

only the LTM8025, two capacitors and two resistors.

Figure 3. The LTM8025 boasts high efficiency.

VIN VOUT

VIN VOUT

3.6V TO 24V 1.8V AT 3A

RUN/SS AUX

BIAS LTM8025 SHARE PGOOD

RT ADJ SYNC GND

Figure 4. The LTM8025 can produce low voltages from a wide input range.

Linear Technology Magazine • September 2009