Dual µModule DC/DC Regulator Produces High Efficiency 4A Outputs from a 4.5V to 26.5V Input Design Note 474 Alan Chern Dual System-in-a-Package Regulator Systems and PC boards that use FPGAs and ASICs are often very densely populated with components and ICs. This dense real estate (especially the supporting circuitry for FPGAs, such as DC/DC regulators) puts a burden on system designers who aim to simplify layout, improve performance and reduce component count. A new family of DC/DC μModule ® regulator systems with multiple outputs is designed to dramatically reduce the number of components and their associated costs. These regulators are designed to eliminate layout errors and to offer a ready-made complete solution. Only a few external components are needed since the switching controllers, power MOSFETs, inductors, compensation and other support components are all integrated within the compact surface mount 15mm × 15mm × 2.82mm LGA package. Such easy layout saves board space and design time by implementing high density point-of-load regulators. The LTM®4619 switching DC/DC μModule converter regulates two 4A outputs from a single wide 4.5V to 26.5V input voltage range. Each output can be set between 0.8V and 5V with a single resistor. In fact, only a few components are needed to build a complete circuit (see Figure 2). Figure 2 shows the LTM4619 μModule regulator in an application with 3.3V and 1.2V outputs. The output voltages can be adjusted with a value change in RSET1 and RSET2. Thus, the final design requires nothing more than a few resistors and capacitors. Flexibility is achieved by pairing outputs, allowing the regulator to form different combinations such as single input/dual independent outputs or single input/parallel single output for higher maximum current output. dn474 F01 L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and μModule are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Figure 1. The LTM4619 LGA Package Is Only 15mm × 15mm × 2.82mm and Houses Dual DC/DC Switching Circuitry, Inductors, MOSFETs and Support Components 4.5V TO 26.5V 10μF s2 VIN RSET1 121k INTVCC VFB1 22pF VOUT1 1.2V/4A MODE/ PLLIN 100μF 0.1μF COMP1 LTM4619 FREQ/ PLLFLTR VFB2 COMP2 VOUT1 VOUT2 TK/SS1 TK/SS2 RUN1 PGOOD RUN2 SGND PGND EXTVCC RSET2 19.1k 22pF 100μF VOUT2 3.3V/4A 0.1μF dn474 F02 Figure 2. 4.5V to 26.5V Input to Dual 3.3V and 1.2V Outputs with 4A Maximum Output Current Each 01/10/474 The efficiency of the system design for Figure 2 is shown in Figure 3 and power loss is shown in Figure 4, both at various input voltages. Efficiency at light load operation can be improved with selective pulse-skipping mode or Burst Mode® operation by tying the mode pin high or leaving it floating. Multiphase Operation for Four or More Outputs For a 4-phase, 4-rail output voltage system, use two LTM4619s and drive their MODE_PLLIN pins with a LTC ®6908-2 oscillator, such that the two μModule devices are synchronized 90° out of phase. Reference Figure 21 in the LTM4619 data sheet. Synchronization also lowers voltage ripple, reducing the need for high voltage capacitors whose bulk size consumes board space. The design delivers four different output voltage rails (5V, 3.3V, 2.5V and 1.8V) all with 4A maximum load. Conclusion The LTM4619 dual output μModule regulator makes it easy to convert a wide input voltage range (4.5V to 26.5V) to two or more 4A output voltage rails (0.8V to 5V) with high efficiency and good thermal dissipation. Simplicity and performance are achieved through dual output voltage regulation from a single package, making the LTM4619 an easy choice for system designs needing multiple voltage rails. 95 4.0 90 3.5 24VIN 12VIN 6VIN 12VIN 24VIN 3.0 POWER LOSS (W) 85 EFFICIENCY (%) Thermal Performance Exceptional thermal performance is shown in Figure 5 where the unit is operating in parallel output mode; single 12VIN to a single 1.5VOUT at 8A. Both outputs tied together create a combined output current of 8A with both channels running at full load (4A each). Heat dissipation is even and minimal, yielding good thermal results. If additional cooling is needed, add a heat sink on top of the part or use a metal chassis to draw heat away. 80 75 70 6VIN 2.5 2.0 1.5 1.0 65 0.5 0 60 0 1 2 3 CURRENT (A) 4 5 0 dn474 F03 Figure 3. Efficiency of the Circuit in Figure 2 at Different Input Voltage Ranges for 3.3V and 1.2V Outputs 1 2 3 CURRENT (A) 4 5 dn474 F04 Figure 4. Power Loss of the Circuit in Figure 2 at Different Input Voltages for 3.3V and 1.2V Outputs dn474 F05 Figure 5. LTM4619: Exceptional Thermal Performance of a Paralleled Output μModule Regulator (12VIN to Paralleled 1.5VOUT at 8A Load) Data Sheet Download www.linear.com For applications help, call (408) 432-1900, Ext. 2593 Linear Technology Corporation dn474 LT/TP 1110 116K • PRINTED IN THE USA FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2009 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ●