feature ofthe SEPIC topology is that, unlike a typical boost con-verter, there is no DC path from the input to the output.This means that when the LT1373 is shut down, the loadis completely disconnected from the input power source.Figure 2 shows that the 3.3V SEPIC converter maintainsreasonable efficiency over two decades of output loadcurrent even though 3.3V circuits typically have low effi-ciency due to catch diode losses., LTC and LT are registered trademarks of Linear Technology Corporation. LT1373VINVC12C1, C3: AVX TPSD 107M010R0100 C2: TOKIN 1E225ZY5U-C203-F L1: COILTRONICS CTX33-2, SINGLE INDUCTOR WITH TWO WINDINGS 8546, 7GNDFBDN108 F01VSWS/SD1 MBRS130LT3C1 100mF 10VC4 0.01mFC2 2.2mFR1 5kR3 24.9k 1% R2 41.2k 1% VOUT 3.3VONOFFL1A 33mH L1B 33mH C3 100mF 10V++SINGLE Li-Ion CELL+ datasheet. For parts similar to the LT1373 with higher switch-ing frequencies (500kHz and 1MHz), consult the LT1372/LT1377 data sheet. LT1373S/S5824DN108 F0316, 7C1 0.01mFR1 2kC2 100mF+C3 100mFL1 10mHD1D2D3VCVSWSINGLE Li-Ion CELLL1: SUMIDA CD54-100 C2 TO C5: AVX TPSD 107M010 D1 TO D3: MBRS130LT3FBVINGNDR2 75k 1%R3 24.9k 1%++C5 100mFR4 24k+C4 100mF5V 5V NEGATIVE LOAD CURRENT (mA)0NEGATIVE OUTPUT VOLTAGE (V) 5.0 5.480DN108 F04 4.6 4.2 4.8 5.2 4.4 4.0 3.82040601090305070100IN = 3V200mA400mAFigure 5. Dual Output Efficiency POSITIVE LOAD CURRENT (mA)550EFFICIENCY (%)80901001050100500DN108 F057060IN = 4VIN = 3VOF 5V CURRENTFigure 3. Single Li-Ion to 5V advertisement250kHz, 1mA IQ Constant Frequency Switcher TamesPortable Systems Power Design Note 108Bob EssaffFigure 1. Single Li-Ion Cell to 3.3V SEPIC ConverterDC-to-DC power conversion remains one of the toughesttasks for portable system designers. Dealing with variousbattery technologies and output voltage requirementsdictate the need for c For literature on our Switching Regulators,call 1- Design Note