advertisement Tiny and Efficient Boost Converter Generates 5V at 3A from 3.3V Bus – Design Note 280 Dongyan Zhou applications, Burst Mode® operation can be disabled when the SYNC/MODE pin is pulled low or driven by an external clock. The LTC1700 can be synchronized to an external clock ranging from 400kHz to 750kHz. Introduction Circuits that require 5V remain popular despite the fact that modern systems commonly supply a 3.3V power bus, not 5V. The tiny LTC®1700 is optimized to deliver 5V from the 3.3V bus at very high efficiency, though it can also efficiently boost other voltages. The small MSOP package and 530kHz operation promote small surface mount circuits requiring minimal board space, perfect for the latest portable devices. By taking advantage of the synchronous rectifier driver, the LTC1700 provides up to 95% efficiency. To keep light load efficiency high in portable applications, the LTC1700 draws only 180μA in sleep mode. The LTC1700 features a start-up voltage as low as 0.9V, adding to its versatility. 3.3V Input, 5V/3A Output Boost Regulator Figure 1 shows a 3.3V input to 5V output boost regulator which can supply up to 3A load current. Figure 2 shows that the efficiency is greater than 90% for a load current range of 200mA to 3A and stays above 80% all the way down to a 3mA load. C2 is a tantalum capacitor providing bulk capacitance to compensate for possible long wire connections to the input supply. In applications where the regulator’s input is connected very close to a low impedance supply, this capacitor is not needed. The LTC1700 uses a constant frequency, current mode PWM control scheme. Its No RSENSE ™ feature means the current is sensed at the main MOSFET, eliminating the need for a sense resistor. This saves cost, space and improves efficiency at heavy loads. For noise-sensitive L1 3.2μH 470pF 22k 2 SGND SW ITH BG 270pF R1 316k 0.1% C3 22μF M1 LTC1700 470pF 4 R2 100k 1% 3 5 RUN/SS VFB PGND TG SYNC/MODE VOUT 9 6 C2 68μF 6.3V + C4 470μF VIN 3.3V ±10% 100 VIN = 3.3V VOUT = 5V VOUT 5V/3A 90 80 70 60 7 50 DN280 F01 C1, C3: TAIYO YUDEN CERAMIC JMK325BJ226M C2: AVX TAJB686K006R C4: SANYO POSCAP 6TPB470M L1: SUMIDA CEP1233R2 M1: INTERNATIONAL RECTIFIER IR7811W M2: SILICONIX Si9803 Figure 1. 3.3V to 5V, 3A Boost Regulator 03/02/280_conv + M2 10 8 C1 22μF EFFICIENCY (%) 1 L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks and No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. 40 1 10 100 1000 LOAD CURRENT (mA) 10000 DN280 F02 Figure 2. Efficiency of the Figure 1 Circuit the increased gate capacitance. MOSFETs with lower than 2.5V gate threshold voltages are recommended. The LTC1700 is also an ideal device for single cell Li-Ion battery to 5V applications. 2-Cell Input, 3.3V/1A Output Regulator In digital cameras and other battery-powered devices, the LTC1700 makes for a high efficiency boost regulator in a small package. Figure 3 shows a 2-alkaline cell to 3.3V output circuit. This circuit can supply 1A maximum output current. Figure 4 shows the efficiency at different battery voltages. Efficiency of this circuit peaks at 93%. If a lower RDS(ON) MOSFET (such as Si6466) is used for M1, the maximum output current can be increased to 1.4A with about a 2% reduction in efficiency due to L1 3.3μH 470pF 33k 2 SGND ITH 100pF BG 8 30.1k 1% 4 3 100pF 5 RUN/SS PGND VFB TG SYNC/MODE VOUT + C2 68μF 6.3V VIN 2V TO 3V 100 M2 10 C3 22μF M1 LTC1700 470pF 52.3k 1% SW C1 10μF + C4 330μF 6.3V VOUT 3.3V/1A 9 6 VOUT = 3.3V VIN = 3V 90 EFFICIENCY (%) 1 Conclusion The LTC1700 boost controller brings high efficiency and small size to low voltage applications. Its features are ideally suited to both battery-powered and linepowered applications. 80 VIN = 2.5V VIN = 2V 70 60 7 50 DN280 F03 C1: TAIYO YUDEN CERAMIC JMK316BJ106ML C2: AVX TAJB686K006R C3: TAIYO YUDEN CERAMIC JMK325BJ226M C4: SANYO POSCAP 6TPB330M L1: MURATA LQN6C M1: SILICONIX Si9804 M2: SILICONIX Si9803 40 1 10 100 LOAD CURRENT (mA) 1000 DN280 F04 Figure 4. Efficiency of the Figure 3 Circuit Figure 3. 2-Cell to 3.3V, 1A Boost Regulator Data Sheet Download www.linear.com Linear Technology Corporation For applications help, call (408) 432-1900 dn280f_conv LT/TP 0302 341.5K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2002