MIC38300 : HELDO™ 3A High Efficiency Low Dropout Regulator - Micrel - #9

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Micrel, Inc. MIC38300 May 2009 9 M9999-051509-C case, inductor selection becomes increasingly critical in efficiency calculations. As the inductors are reduced in size, the DC resistance (DCR) can become quite significant. The DCR losses can be calculated as follows: L_PD = IOUT 2 × DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows; 100 _ _ 1 × . .. . .. . .. . .. × + × = - OUT OUT D OUT OUT V I L P Efficiency Loss V I Efficiency loss due to DCR is minimal at light loads and gains significance as the load is increased. Inductor selection becomes a trade-off between efficiency and size in this case. Current Sharing Circuit The following circuit allows two MIC38300 HELDO regulators to share the load current equally. HELDO1 senses the output voltage at the load, on the other side of a current sense resistor. As the load changes, a voltage equal to the output voltage, plus the load current times the sense resistor, is developed at the VOUT terminal of HELDO1. The Op-Amp (MIC7300) inverting pin senses this voltage and compares it to the voltage on the VOUT terminal of HELDO2. If the current through the current sense of HELDO2 is less than the current through the current sense of HELDO1, the inverting pin will be at a higher voltage than the non-inverting pin and the Op-Amp will drive the FB of HELDO2 low. The low voltage sensed on HELDO2 FB pin will drive the output up until the output voltage of HELDO2 matches the output voltage of HELDO1. Since VOUT will remain constant and both HELDO VOUT terminals and sense resistances are matched, the output currents will be shared equally Current Sharing Circuit for 6A Output