LINEAR LTM4627 Manual
Contents
1. Figure 3 shows a LTM4627 thermal plot for 12V to 1V at 15A with no airflow or heat sinking The temperature rise is 40 C above 25 c ambient at 65 c The power loss of 3w multiplied by the data sheet specified thermal resistance of 13 C w matches the 40 c rise in the thermal plot The LTIM4627 package has a highly thermal conductive substrate with a layout that is thermally modeled and designed to enhance thermal performance and uni form heat spreading While the package is small it presents enough surface area to a PCB and heat sink to minimize the overall thermal resistance of the solution Figure 4 shows the LTM4627 12V to 1V de rating curve The LTM4627 can operate in higher ambient temperatures with full load capability in a very small form factor Figure 5 shows a 2 phase 30A design uti lizing two parallel LtM4627 pModule regu lators that are clocked 180 out of phase using clock signals from the LTc6908 1 VIN 7V TO 16V ae o arle OUTPUT CURRENT A OLFM NO HEATSINK 200LFM NO HEATSINK 400LFM NO HEATSINK 0 40 50 60 70 80 90 100 110 120 AMBIENT TEMPERATURE C Figure 4 Derating curves for the LTM4627 converting 12V to 1V Current sharing is well balanced during both steady state pc load and dynamic transients The accurate remote sense amplifier yields outstanding voltage accu racy at the load point For even higher out put2. ackage The LTM4627 inte grates the high performance power path Figure 2 Efficiency of the regulator in Figure 1 100 95 fsw 400kHz 90 85 80 EFFICIENCY 75 70 65 60 38 October 2011 LT Journal of Analog Innovation Figure 3 Thermal plot of the LTM4627 converting 12V to 1V at 15A with no forced air or heat sink and control circuitry thus simplify ing the design to a few external bulk capacitors and a few small resistors The LTM4627 features include fully dif ferential remote sensing output voltage tracking and soft start high efficiency at light loads utilizing the Burst Mode operation or pulse skipping features voltage monitoring and frequency synchronization The LTM4627 uses a current mode architecture which enables multiple Module regulators to run in parallel Figure 5 sharing the load for increased output current with accurate current limit control The LTM4627 pModule regulator is optimized for high efficiency conversion to low output voltages with a complete converter packaged in a small thermally enhanced form factor The input volt age range is 4 5V to 2ov with output voltage programming from o 8V to 5V Figure 2 shows efficiencies of 82 to 83 for 1v at 15A from 5v 8v and 12v inputs This is an efficiency improvement of 6 to 7 over typical and larger solutions or a power loss improve ment of 1 68w in a small form factor
3. currents simply add more LTM4627s CONCLUSION The Lt M4627 pModule regulator is a high performance versatile DC DC converter that can be used in many applications requiring high efficiency over a wide output voltage range The very small form factor and ease of use make the LTM4627 ideal for space constrained designs m INTVec W 30A Figure 5 A 2 phase 30A design based on two parallel LTM4627 Module regulators clocked 180 out of phase For higher output currents simply add more LTM4627s INTVcc CLOCK SYNC yt OUTI 180 PHASE LTC6908 1 GND OUT2 SET MOD October 2011 LT Journal of Analog Innovation 39
4. o O 15A Module Regulator Solves Thermal Problems by Converting 12V to 1V with High Efficiency Eddie Beville Advances in silicon process technology continue to reduce transistor geometries down to historical levels in microprocessors FPGAs and ASICs The power supply voltage levels necessary to power these large complex digital devices also continue to shrink creating unique power supply design challenges One major concern is the power regula tor s conversion efficiency at low output voltages For example a typical high efficiency switching regulator that con verts 12V to 3 3V at 15A has a conver sion efficiency of 93 For practical purposes such a regulator incurs most of its efficiency loss due to IR losses Therefore 93 efficiency for processing 49 5W to the load equates to a 3 72w loss Likewise a low output voltage require ment of 1v at 15A with an efficiency of 76 incurs a power loss of 4 74W Typical high density power solutions are challenged to achieve high efficien cies at low output voltages due to the size constraints of the power stage The power stage must have high performance power MOSFETs and inductors to improve low voltage conversion efficiency not just an increase the solution size In reality many feature laden digital devices have current requirements in the gt 30A range for the low voltage sup ply Thus a 76 efficiency 1v output would incur a 9 48w loss for a 30A load which
5. would certainly cause thermal challenges The thermal problems mul tiply with the number of 30a regula tors required on a system board Unchecked regulator power losses when added to other system power losses create serious thermal chal lenges One issue is that small geometry ASIC or FPGA leakage currents rise with Figure 1 A complete 1V at 15A converter requires only a few components around the LTM4627 Module regulator which comes in a thermally enhanced 15mm x 15mm x 4 32mm package VIN 4 5V TO 16V system temperature thus compromis ing system performance and reliability One possible solution is to use a power converter module that can deliver signifi cantly higher output power than necessary for the application and run it at an output current point that maximizes efficiency Of course overly large solutions are not feasible in space constrained systems and the current limit of this solution is much higher than the required current Another solution is to use a discrete power converter that is optimized for low output voltage efficiency But again space constraints and component sourcing can be challenging Another challenge with a discrete design is how to effectively cool it and heat sink the various discrete power components which have different heights UMODULE SOLUTION Figure 1 shows a complete 1 0v at 15A con verter that uses the LTM4627 pModule regulator housed in a 15mm x 15mm x 4 32mm p
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LINEAR LTM4627 Manual