4-Phase Boost Converter Delivers 384W with no Heat Sink Design Note 453 Victor Khasiev Introduction High power boost converters are becoming increasingly popular among designers in the automotive, industrial and telecom industries. When power levels of 300W or more are required, high efficiency (low power loss) is imperative in the power train components to avoid the need for bulky heat sinks and forced-air cooling. Interleaving power stages (multiphase operation) improves efficiency and reduces ripple voltage and currents in both the input and output capacitors, allowing the use of smaller filter components. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. L1 19.4μH D1 PDS760 VIN 5V TO 18V L2 19.4μH 3×10μF 84.5k D2 PDS760 HAT2266H 24.9k 1nF U1 1 2 3 VOUT 4 66.5k 475k 5 0.1μF 6 68k 7 12.4k 8 10nF 9 220pF Q1 10 11 12 DMAX 3V8 SLOPE RUN LTC3862 BLANK VIN INTVCC PH/MODE NC FREQ SS PGND ITH G1 SENSE1+ FB 10 24 10nF 6m 21 20 19 15 VOUT 48V 8A 1μF 4.7μF 17 4×120μF 18 23 + 14×6.8μF HAT2266H Q2 – 22 SENSE1 SGND G2 CLKOUT 16 10 + 13 SYNC SENSE2 PLLFLTR SENSE2– 10nF 6m 14 D3 PDS760 L3 19.4μH VIN L4 19.4μH 3×10μF D4 PDS760 HAT2166H Q3 1nF U2 1 2 3 4 66.5k 5 6 220pF 7 8 9 10 11 12 10nF 10k DMAX 3V8 SLOPE RUN LTC3862 BLANK PH/MODE FREQ SS ITH VIN INTVCC NC PGND G1 6m 20 19 15 1μF 4.7μF 17 18 23 SENSE1+ SGND 22 SENSE1– G2 10nF 21 FB CLKOUT 10 24 HAT2166H Q4 16 SYNC SENSE2+ 13 PLLFLTR SENSE2– 14 L1 TO L4: PAPA2050-193 10 10nF 6m DN453 F01 Figure 1. A 4-Phase Boost Converter Based on the LTC3862 Produces 48V at 8A from a 5V to 18V Input 10/08/453 The power train includes four inductors L1-L4, four MOSFETs Q1-Q4, four diodes D1-D4, along with the input and output filter capacitors. The ITH, FB, SS and RUN pins of the two controllers are connected together, which forces current share balancing and consistent start up timing between the phases, and forces both controllers to turn on at the same input voltage. This converter can deliver 8A at 48V continuously from a 12V to 18V input. It can even support the 48V output with input voltages down to 5V, at a reduced output current. Figure 3 shows the converter efficiency above 96% for much of the load range. The transient response to a 3A load step as shown in Figure 4 has only a 100mV deviation from nominal. Up to 12 power stages can be paralleled and clocked out-of-phase for even higher power applications. The LTC3862 has an input voltage range of 4V to 36V and an output voltage that is dependent upon the choice of external components, making it an excellent choice for 12V automotive high power boost converter applications such as audio amplifiers and fuel injection systems. Conclusion The LTC3862 2-phase controller is a powerful building block for multiphase boost converter applications that demand high efficiency, low power loss, reduced ripple voltage and currents, and have a small solution size without the need for forced-air cooling or heat sinks. 97.8 12VIN 14VIN 18VIN 97.6 97.4 EFFICIENCY (%) 384W Boost Converter Figure 1 shows a 4-phase boost converter using two 2-phase LTC®3862 current mode controllers configured in a master-slave configuration (as described in the LTC3862 data sheet). U1 is the master controller; it generates the clock signal that serves to synchronize the two controllers. Synchronization is achieved by connecting U1’s CLKOUT pin to U2’s SYNC pin and terminating the PLLFLTR pin of U2 with a lowpass filter. Each controller operates with a 180° phase shift between its two channels, and there is a 90° phase shift between the two controllers as defined by the state of U1’s PHASEMODE pin, to form an interleaved 4-phase system as shown in Figure 2. 97.2 97.0 96.8 96.6 96.4 96.2 96.0 2 3 4 5 IO (A) 6 8 7 DN453 F03 Figure 3. Efficiency vs Output Current Input Voltage for Multiple VIN. 50V/DIV Q1 50V/DIV Q2 50V/DIV Q3 50V/DIV Q4 1μs/DIV VOUT 100mV/DIV IOUT 2A/DIV DN453 F02 Figure 2. Timing Diagram Showing 4-Phase Operation 2ms/DIV DN453 F04 Figure 4. Transient Response for a Current Load Step from 2A to 5A. Data Sheet Download For applications help, call (408) 432-1900, Ext. 2593 www.linear.com Linear Technology Corporation dn453f LT/TP 1008 246K • PRINTED IN THE USA FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ●