advertisement SOT-23 DC/DC Converters Generate Up to ±35V Outputs and Consume Only 20µA of Quiescent Current – Design Note 223 Bryan Legates Today’s portable devices need small power supply solutions that operate with a minimum of supply current. To meet these needs, Linear Technology introduces the LT®1615, LT1615-1, LT1617 and LT1617-1 micropower SOT-23 DC/DC converters. With an input voltage range as low as 1V and an output voltage range as high as ±35V, these devices provide considerable power supply design flexibility. The LT1615 and LT1615-1 are designed to regulate positive output voltages, whereas the LT1617 and LT1617-1 are designed to directly regulate negative output voltages without the need for feedback level-shifting circuitry. The LT1615 and LT1617 have a 350mA current limit and a minimum input voltage of 1.2V, whereas the LT1615-1 and LT1617-1 have a lower, 100mA current limit and a minimum input voltage of 1V. All four converters use tiny, low profile inductors and capacitors to minimize the overall system footprint and cost. With a quiescent current of only 20μA and a shutdown current of 0.5μA, these devices squeeze the most life out of any battery-powered application. ±20V Dual-Output Converter with Output Disconnect Today, most portable devices use a liquid crystal display (LCD). Different manufacturers require substantially different bias voltages for their LCDs. Typically, a single 9V to 25V supply is needed (either positive or negative), but some LCDs require both a positive and negative supply. Figure 1 shows a ±20V dual-output converter ideally suited for LCD bias applications needing both supplies. Both outputs are developed using charge pumps, so both are disconnected from the input when the LT1617 is turned off. Because the supplies are generated in the same manner, this circuit features excellent cross regulation: for a 5× difference in output currents, the positive and negative output voltages differ less than 1%; for a 10× difference, they differ less than 2%. A similar circuit can be implemented using the LT1615 if the regulation of the positive output is more important. As shown in Figure 2, efficiency reaches 78% with a fresh 4-cell alkaline battery. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. D3 C5 0.1μF D2 C4 0.1μF L1 10μH 5 1 VIN SW 85 D1 –20V 4mA 4 SHDN C2 1μF 100pF D4 267k LT1617 C1 4.7μF NFB 3 GND 80 VIN = 6V 75 VIN = 3.3V 70 65 60 24.9k 2 C1: TAIYO YUDEN LMK316BJ475 C2, C3: TAIYO YUDEN TMK316BJ105 C4, C5: TAIYO YUDEN UMK212BJ104 L1: MURATA LQH3C100K24 D1, D2, D3, D4: MOTOROLA MBR0530 55 (408) 573-4150 (408) 573-4150 (408) 573-4150 (814) 237-1431 (800) 441-2447 Figure 1. ± 20V Dual Output Converter with Output Disconnect 02/00/223_conv 90 EFFICIENCY (%) VIN 1.5V TO 6V 20V 4mA C3 1μF DN223 F01 50 0.1 1 10 LOAD CURRENT FOR EACH OUTPUT (mA) DN223 F02 Figure 2. ± 20V Dual Output Converter Efficiency 24V Boost Converter Figure 3 shows a circuit ideal for LCD applications needing only a positive bias voltage. This 24V boost converter delivers 10mA from a nearly discharged single Li-Ion cell. An input voltage as low as 1.5V can be used with this converter, but the output current capability reduces to 5mA. Converter efficiency is shown in Figure 4. L1 10μH VIN 2.5V TO 6V 5 D1 24V 10mA 1 VIN SW C1 4.7μF SHDN FB L1 22μH VIN 1V TO 6V 1.07M C2 1μF LT1615 4 1-Cell to 3V Boost Converter A 1-cell alkaline to 3V boost converter using the LT1615-1 is shown in Figure 6. Capable of providing 15mA of output current, this converter occupies a board area less than 1/4" by 5/16" (less than 0.078 inches2). See Figure 7 for converter efficiency, which reaches 75% with a fresh 1-cell alkaline battery. 3 GND 4 1 VIN SW Figure 3. 24V Boost Converter GND EFFICIENCY (%) 75 (408) 573-4150 (408) 573-4150 (800) 441-2447 (814) 237-1431 L1 4.7μH VIN = 2.5V D1 5 1 VIN SW 4 65 C1 4.7μF 60 100 DN223 F04 100k NFB 357k 3 GND 249k 2 C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN JMK316BJ106 D1: CENTRAL SEMI CMDSH-3 L1: MURATA LQH3C4R7M24 55 1 10 LOAD CURRENT (mA) SHDN 3V 15mA C2 10μF 4.7pF LT1615-1 70 50 0.1 DN223 F05 Figure 5. 1V to 35V Boost Converter VIN 1V TO 1.5V 80 365k 2 90 VIN = 6V C2 1μF 3 FB C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN GMK316BJ105 D1: MOTOROLA MBR0540 L1: MURATA LQH3C220K34 DN223 F03 85 35V 500μA 10M SHDN C1 4.7μF 57.6k (408) 573-4150 (408) 573-4150 (800) 441-2447 (814) 237-1431 5 LT1615-1 2 C1: TAIYO YUDEN LMK316BJ475 C2: TAIYO YUDEN TMK316BJ105 D1: MOTOROLA MBR0530 L1: MURATA LQH3C100K24 D1 (408) 573-4150 (408) 573-4150 (800) 441-2447 (814) 237-1431 DN223 F06 Figure 6. 1-Cell Alkaline to 3V Boost Converter Figure 4. 24V Boost Converter Efficiency 80 Data Sheet Download www.linear.com Linear Technology Corporation VIN = 1.5V 75 VIN = 1V EFFICIENCY (%) 1V to 35V Boost Converter The circuit in Figure 5 shows the impressive input and output voltage range of the LT1615-1. As shown, the circuit will work from one to four alkaline cells or a single cell Li-Ion battery. The maximum input voltage for this circuit is limited by the 6.3V voltage rating on the input capacitor, C1. The LT1615-1 can operate with an input voltage as high as 15V. The output current is limited by the 1V minimum input (this converter can provide 2mA with a 3V input). If a larger output current is needed, but operation from a 1V input is not required, use an LT1615 in place of the LT1615-1 to obtain a 3× increase in maximum output current. 70 65 60 55 50 0.1 1 10 LOAD CURRENT (mA) DN223 F07 Figure 7. 1-Cell to 3V Boost Converter Efficiency For applications help, call (408) 432-1900 dn223f_conv LT/TP 0200 340K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2000