L DESIGN IDEAS Self-Contained 3A µModule Buck Regulator Produces 0.8V–24V Output by David Ng from 3.6V–36V Input Introduction AUX GND Ask any group of engineers, “What would you do with a 3A DC/DC converter?” and you will probably get a wide range of answers—from powering a DSP rail at 1.8V to running a bank of 24V switching I/O. Typically, these two particular applications would require completely different DC/DC controller ICs and topologies. However, the LTM8025 µModule DC/DC converter can satisfy the requirements of these and just about any other 3A applications. The LTM8025 3A µModule DC/DC buck converter operates from 3.6V to 36V inputs to produce output voltages as low as 0.8V and as high as 24V. Furthermore, the LTM8025 features single cycle Burst Mode® operation, so it is able to handle a wide range of load currents, from no load to 3A, with minimum ripple. Easy Layout PGOOD RT RADJ GND SYNC SHDN BIAS VOUT VIN COUT CIN GND THERMAL VIAS TO GND Figure 1. Layout is easy with the LTM8025. The LTM8025 integrates the controller, control circuitry, inductor, power switch and rectifier all into a single IC form factor 15mm × 9mm × 4.32mm package. This LGA package is RoHS (e3) compliant, and features gold pads for easy assembly in both leaded and unleaded solder processes. The LTM8025’s high level of integration simplifies the design of just about any 3A power supply. Just add two resistors, input and output capacitance to make a complete power supply. Layout is easy, as shown in Figure 1. Figures 2 and 3 show the schematic and efficiency of the LTM8025 producing 12V bus power from a 24V source, while Figure 4 shows the LTM8025 producing 1.8V from an input range of 3.6V to 36V. Versatile Feature Set The LTM8025 may be operated over a wide frequency, from 200kHz to 2.4MHz, and may be synchronized to an external clock source through the SYNC pin. The LTM8025 start-up is controlled through its RUN/SS pin, which also serves to put the part into continued on page 42 100 VIN 4.7µF VOUT RUN/SS 90 BIAS PGOOD RT 22µF ADJ SYNC VIN = 24V AUX LTM8025 SHARE 47.5k VOUT 12V AT 3A EFFICIENCY(%) VIN* 22V TO 36V GND 34.8k 80 70 60 50 *RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS 40 Figure 2. A complete 12V at 3A power supply requires only the LTM8025, two capacitors and two resistors. 0 500 1000 1500 2000 2500 OUTPUT CURRENT (mA) 3000 Figure 3. The LTM8025 boasts high efficiency. VIN 3.6V TO 24V VIN 10µF BIAS AUX 300µF LTM8025 SHARE PGOOD RT 147k VOUT 1.8V AT 3A VOUT RUN/SS ADJ SYNC GND 383k Figure 4. The LTM8025 can produce low voltages from a wide input range. 40 Linear Technology Magazine • September 2009 L NEW DEVICE CAMEOS The LT4356-2 is offered in 12-pin DFN and 16-pin SO packages, while the LT4356-3 is available in 12-pin DFN, 16-pin SO, and 10-pin MSOP packages. Dual Output Synchronous DC/DC Controller Draws Only 170µA in Battery-Powered Systems The LTC3868/-1 is a low quiescent current, 2-phase dual output synchronous step-down DC/DC controller. The LTC3868/-1 draws only 170µA with one output active and only 300µA when both outputs are active, making it ideal for battery-powered applications. With both outputs shut down, the LTC3868/-1 draws only 8µA. The LTC3868/-1 has an input supply range of 4V to 24V and each output can be set from 0.8V to 14V at output currents up to 20A. With efficiency as high as 95%, a LTC3868/-1 based DC/DC converter is well suited for powering industrial and medical devices, along with portable instruments, notebook and netbook computers. The LTC3868/-1 operates with a user-adjustable, fixed frequency between 50kHz and 900kHz, and LTM8025, continued from page 40 a low power off state in which the part draws less than 1µA. Furthermore, the part comes with a PGOOD pin to indicate that the output is within 90% of its target voltage. Parallel Multiple LTM8025s for High Current Capability The LTM8025 is equipped with a SHARE pin to allow parallel operation for applications requiring more than 3A load current. Figure 5 shows two synchronized LTM8025’s providing 2.5VOUT at 5.6A. Conclusion The highly versatile LTM8025 3A µModule DC/DC buck converter is easy to use and fits just about any step-down regulator need. Its wide input and output ranges and high level of integration reduce design effort and associated costs. L 42 can be synchronized to an external clock from 75kHz to 850kHz using its phase-locked-loop (PLL). The user can select from continuous operation, pulse-skipping and low ripple Burst Mode operation during light loads. These parts also safely start up with a prebiased load by powering up and down in pulse-skipping mode. The LTC3868/-1’s 2-phase operation reduces input capacitance requirements and its current mode architecture provides easy loop compensation and fast transient response. Both outputs have adjustable softstart to control the turn-on time, and the output overload protection feature latches off the converter until the input voltage is recycled. The LTC3868/ LTC3868-1 also features a tight ±1.5% reference voltage accuracy over a –40°C to 85°C operating temperature range. The LTC3868 is the fully featured part with additional functions beyond the LTC3868-1 including a clock out, phase modulation, two power good outputs and adjustable current limit. The LTC3868 is offered in a 32-lead 5mm × 5mm QFN package and the VIN* 4.1V TO 36V LTC3868-1 in a 28-pin SSOP or 4mm × 5mm QFN-28 packages. Boost & Inverting DC/DC Converter for Active Matrix OLED & CCD Bias The LT3582, LT3582-5 and LT358212 dual channel DC/DC converters that deliver both positive and negative outputs required in many biasing applications such as active matrix OLED (organic light-emitting diode) displays as well as CCD (charge coupled device) applications. The LT3582/-5/-12 offer an I2C interface that can dynamically program output voltages, power sequencing and output voltage ramps as the application requires. Alternatively, these parameters can be set in manufacturing and made permanent via the built in nonvolatile OTP (one time programmable) memory. The LT3582’s positive output voltage can be set between 3.2V and 12.775 in 25mV steps, whereas the negative output can be set between –1.2V and –13.95V in 50mV steps. The LT3582-5 and LT3582-12 are pre-configured with ±5V and ±12V outputs respectively, useful in many signal conditioning applications. L VIN VOUT 2.5V AT 5.6A VOUT RUN/SS AUX LTM8025 SHARE BIAS 3V PGOOD 2.2µF RT ADJ SYNC 137k GND 113k OPTIONAL SYNC VIN VOUT RUN/SS AUX LTM8025 SHARE BIAS 300µF PGOOD 2.2µF RT 137k ADJ SYNC GND *RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS NOTE: SYNCHRONIZE THE TWO MODULES TO AVOID BEAT FREQUENCIES, IF NECESSARY. OTHERWISE, TIE EACH SYNC TO GND Figure 5. Two LTM8025s can be operated in parallel for more than 3A load current. Linear Technology Magazine • September 2009