LINEAR dn359f handbook
Contents
1. advertisement DESIGN NOTES Dual DC DC Converter with Integrated Schottkys Generates 40V Outputs and Consumes Only 40uA Quiescent Current Design Note 359 David Kim Introduction As portable devices become more sophisticated and require higher display resolution there is an increased demand for accurate high voltage bias supply solutions with wide input and output voltage ranges The traditional methods of using arrays of capacitors to implement a charge pump or a bulky and expensive transformer no longer meet the accuracy and size requirements of today s portable devices The LT 3463 is both accurate and compact It fits both a positive output converter plus a negative output converter into atiny 3mm x 3mm DFN package including Schottky diodes and switches capable of 250mA 400mA on the negative channel of the LT3463A The LT3463 works in a wide range of applications due to its 2 3V to 15V input voltage range and output capability to 40V Each converter is designed to operate with a quiescent current of only 20uA which drops to less than uA in shutdown making the LT3463 solution ideal for battery powered portable applications Vin 10uH D1 DIODES INC B0540W L1 L2 MURATA LQH32CN100K53 Figure 1 Dual Output 20V Converter DN359 F01 Dual Output 20V Converter Figure 1 shows a 20V LCD bias voltage supply using the LT3463 This circuit generates both posi2. plications requiring multiple posi tive and negative high output voltages wide input voltage range low quiescent current small circuit size and accu rate output regulation For applications help call 408 432 1900 Ext 2759 Linear Technology Corporation 1630 McCarthy Blvd Milpitas CA 95035 7417 408 432 1900 FAX 408 434 0507 www linear com dn359f LT TP 0305 305K PRINTED IN THE USA LY MUR LINEAR TECHNOLOGY CORPORATION 2005
3. rcuit is designed to operate from a Li lon battery or two alkaline cells down to 2 4V c3 0 22uF L1 L2 MURATA LQH32CN100K53 pnaso roa D1 DIODES INC B0540W Figure 3 2 7V to 40V Dual Output Converter CCD Sensor Bias Supply The circuit in Figure 4 shows a CCD sensor bias supply for acellular camera phone application The two outputs 15V and 8V are generated from a Li lon battery input With a minimum input voltage of 3 3V the circuit is designed to output 15V at 10mA and 8V at 40mA to accommodate the maximum current consumption of the CCD sensor The low power consumption of the LT3463 and its small circuit size also make this solution ideal as a general purpose TFT display bias supply for portable devices Figure 5 shows the efficiency and power loss data for the circuit Data Sheet Download http www linear com Li 10uH 2 7V TO 5V T SW1 Vouti 1 FB1 LT3463A Vege FB2 swe D2 D1 DIODES INC BO540W L1 L2 MURATA LQH32CN100K53 C3 nT DN359 FO4 pej O m m3 1206 n n E Figure 4 CCD Sensor Bias Supply 80 240 75 200 70 65 EFFICIENCY 60 55 Y 0 100 LOAD CURRENT mA DN359 FOS Figure 5 Efficiency and Power Loss for the Circuit in Figure 4 Conclusion The LT3463 LT3463A are ideal solutions for high resolu tion portable display ap
4. tive and nega tive 20V outputs from a Li lon battery Low profile inductors and capacitors keep the circuit under 9mm x 9 5mm x 1 2mm making this circuit ideal for small wireless devices such as cellular phones or DSCs This design can produce 20V at 9mA from a 2 7V input and up to 20mA from a 5V input The efficiency shown in Figure 2 exceeds 70 overa wide load current range reach ing 75 at 20mA The LT3463 s constant off time archi tecture allows 20uA quiescent current operation for each output making the LCD bias circuit efficient even at 100uA load current This circuit can accommodate different load voltages as the LCD bias voltage varies for different manu facturers typically 9V 25V 4J LTC and LT are registered trademarks of Linear Technology Corporation All other trademarks are the property of their respective owners 80 20V OUTPUT 70 20V OUTPUT EFFICIENCY 60 0 1 1 10 100 LOAD CURRENT mA DN359 F02 Figure 2 Efficiency of Circuit in Figure 1 at Viy 3 6V 03 05 359 Dual Output 40V Converter The circuit in Figure 3 demonstrates the impressive input and output voltage range of the LT3463 As shown the 42V internal switches allow up to 40V output without a transformer or an array of diodes and capacitors The output voltages can be easily changed by adjusting the values of R1 and R3 The ci
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LINEAR dn359f handbook