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LM2940J 데이터시트(PDF) 4 Page - List of Unclassifed Manufacturers |
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LM2940J 데이터시트(HTML) 4 Page - List of Unclassifed Manufacturers |
4 / 5 page Bay Linear, Inc 2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 989-7144, Fax: (925) 940-9556 www.baylinear.com LM2940/2941 APPLICATION HINTS The Bay Linear LM2941 incorporates protection against over-current faults, reversed load insertion, over temperature operation, and positive and negative transient voltage. However, the use of an output capacitor is required in order to insure the stability and the performances. Thermal Consideration Although the LM2941 offers limiting circuitry for overload conditions, it is necessary not to exceed the maximum junction temperature, and therefore to be careful about thermal resistance. The heat flow will follow the lowest resistance path, which is the Junction- to-case thermal resistance. In order to insure the best thermal flow of the component, a proper mounting is required. Note that the case of the device is electrically connected to the output. The case has to be electrically isolated, a thermally conductive spacer can be used. However do not forget to consider its contribution to thermal resistance. Assuming: VIN = 10V, VOUT = 5V, IOUT = 1.5A, TA = 90°C, θCASE= 1°C/W (no external heat sink, no wind) Power dissipation under these conditions PD = (VIN – VOUT) * IOUT = 7.5W Junction Temperature TJ = TA + PD * (θCASE+ θJC) For the Control Section TJ = 90°C + 7.5W*(1°C/W + 0.6°C/W) = 102°C 114 °C < TJUNCTION MAX for the control section. For the Power Section TJ = 90°C + 7.5W*(1°C/W + 1.6°C/W) = 104.5°C 109.5 °C < TJUNCTION MAX for the power transistor. In both case reliable operation is insured by adequate junction temperature. Capacitor Requirements The output capacitor is needed for stability and to minimize the output noise. The required value of the capacitor varies with the load. However, a minimum value of 10 µF Aluminum will guarantee stability over load. A tantalum capacitor is recommended for a fast load transient response. If the power source has high AC impedance, a 0.1 µF capacitor between input & ground is recommended. This capacitor should have good characteristics up to 250 kHz. Minimum Load Current To ensure a proper behavior of the regulator at light load, a minimum load of 5mA for LM2941 is required. Adjustable Regulator Design B29152/53 are adjustable regulators and maybe programmed for any value between 1.25V and 26V using two resistors. The relation between the resistors is given by: R1=R2 (VOUT/1.240 –1) Resistors have a large value up to 1m Ω in order to reduce the current consumption. This might be interesting in the case of widely varying load currents. Enable Input LM2941 features enable input allowing turning ON & OFF the device. EN has been designed to be compatible with TTL/CMOS logic. When the regulator is ON, the current flowing through this pin is approximately 20 µA. 4 5 3 2 1 BAY B2941 V OUT V IN R 1 R 2 Fig. 2 Adjustable Output Voltage Regulator V OUT = VREF X [1 + (R1/ R 2)] For best results, the total series resistance should be small enough to pass the minimum regulator load current 4 5 3 2 1 BAY B2941 V OUT V IN R 1 R 2 Fig. 2 Adjustable Output Voltage Regulator V OUT = VREF X [1 + (R1/ R 2)] For best results, the total series resistance should be small enough to pass the minimum regulator load current BAY B2940 Fig.1 Basic Fixed Output Regulator V OU T V IN BAY B2940 Fig.1 Basic Fixed Output Regulator V OU T V IN |
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