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High Effi ciency 2-Phase Boost Converter Minimizes Input and Output Current Ripple – Design Note 371 Goran Perica

Introduction Switching currents also increase proportional to the Many automotive and industrial applications require output-to-input voltage conversion ratio, so if the input higher voltages than is available on the input power voltage is low, the switching currents can overwhelm a supply rail. A simple DC/DC boost converter suffi ces simple boost converter and generate unacceptable EMI. when the power levels are in the 10W to 50W range, For example, consider Figure 1, a 12V input to 24V, 10A but if higher power levels are required, the limitations output switching converter operating at 300kHz. The of a straightforward boost converter become quickly currents processed by the converter in Figure 1 are apparent. Boost converters convert a low input voltage to shown in the fi rst row of Table 1. The relatively high cur- a higher output voltage by processing the input current rent levels in the switcher are refl ected in high input and with a boost inductor, power switch, output diode and output ripple currents, which results in increased EMI. output capacitor. As the output power level increases, L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks the currents in these components increase as well. of Linear Technology Corporation. All other trademarks are the property of their respective owners.

INPUT 10V TO 23V 22μF 75k L1 w2 4.7μH MBRB2545 13.3k 1 9 OUTPUT RUN VIN 24V 12k LTC1871-7 4.7nF 2 7 HAT2165 10A ITH GATE + 80.6k 4 10 w2 22μF 220μF VOUT FREQ SENSE w6 5 8 100mV/DIV MODE/SYNC INTVCC 0.002Ω 12.4k 3 6 4.7μF VFB GND

DN371 F01b DN371 F01 1μs/DIV 229k L1: COOPER HC3-4R7 ALL CERAMIC CAPACITORS ARE X7R, TDK Figure 1b. Single-Phase Boost Figure 1a. Single-Phase Boost Converter: Can be Converter Output Voltage Ripple Used to Convert 12V Input to 24V, 10A Output

Table 1. Dual-Phase Boost Converter Has Lower Input and Output Ripple Currents and Voltages Than Single-Phase Boost Converter MOSFET OUTPUT OUTPUT OUTPUT OUTPUT INPUT RMS INPUT RIPPLE RMS DRAIN DIODE RMS CAPACITOR CAPACITOR VOLTAGE CURRENT CURRENT CURRENT CURRENT RMS CURRENT FREQUENCY RIPPLE SINGLE- PHASE BOOST 21.1A 4.2AP-P 15.4A 14.4A 10.5A 300kHz 212mV CONVERTER DUAL-PHASE BOOST 20.7A 0.17AP-P 2 × 7.4A 2 × 7.2A 1.9A 600kHz 65mV CONVERTER

09/05/371_conv The circuit shown in Figure 2 performs the same DC/DC a 240W boost supply application, the power dissipation conversion, but with greatly reduced input and output of 12.9W is relatively easy to manage in a well laid out, ripple, signifi cantly reducing EMI, and at a higher ef- large multilayer PCB with some forced airfl ow. fective switching frequency, which allows the use of two 22μF output capacitors versus six 22μF output Conclusion capacitors required in Figure 1. The simple LT3782 dual-phase switching boost con- ver t er impr ove s on singl e - ph a s e a l t er n a t i ve s by a llow ing The trick is the 2-phase boost topology, which inter- high power output with lower ripple currents, reduced leaves two 180° out-of-phase output channels to mu- heat dissipation and a more compact design. tually cancel out input and output ripple current—the results are shown in the second row of Table 1. Each 96 phase operates at 50% duty cycle and the rectifi ed 95 output currents from each phase fl ow directly to the load—namely the low inductor ripple current—so only 94 a small amount of output current (shown in Table 1) is 93 handled by the output capacitors.

EFECIENCY (%) 92 The centerpiece of the design in Figure 2 is the LT®3782 2-phase current mode PWM controller. Current mode 91 operation ensures balanced current sharing between 90 the two power converters resulting in even power dis- 0 2 46810 12 OUTPUT CURRENT (A) DN371 F03 sipation between the power stages. Figure 3. 12V Input to 24V Output Dual-Phase Boost The effi ciency of the dual-phase converter, shown in Converter Effi ciency Figure 3, is high enough that it can be built entirely with surface mount components—no need for heat sinks. In

L1 UPS840 INPUT 10V TO 23V

825k BGATE1 HAT2165 274k 10Ω RUN SEN1P LT3782 10nF

RSET SEN1N 0.004Ω 220μF + DELAY VCC 62k 2.2μF 22μF VOUT DCL GBIAS OUTPUT 100mV/DIV 59k 24V SLOPE GBIAS1 10A 22μF SS GBIAS2 0.004Ω w2 4.7nF DN371 F02b GND SEN2N 1μs/DIV 10nF 10Ω VEE1 SEN2P Figure 2b. Dual-Phase Boost VEE2 BGATE2 HAT2165 15k 220k Converter Output Voltage Ripple 4.7nF UPS840 VC FB L2 100pF 24.9k DN371 F02 L1, L2: PULSE PB2020-153 ALL CERAMIC CAPACITORS ARE X7R TDK Figure 2a. Dual-Phase Boost Converter Reduces EMI and Ripple Currents with a Minimum Input and Output Filtering

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