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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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LM138QML Datenblatt(PDF) 13 Page - Texas Instruments |
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LM138QML Datenblatt(HTML) 13 Page - Texas Instruments |
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13 / 34 page  VIN VOUT ADJ LM138QML GND COUT ‚ 1…F CIN* 0.1…F R1 270 R2 820 CADJ 10…F D1** 1N4002 D2 ‚* 1N4002 VIN VOUT ‚‚ *Needed if device is more than 6 inches from filter capacitors ‚2SWLRQDO±±improves transient response **Recommended if COUT is used ‚‚ ‚*Recommended if CADJ is used 2 I 1 2 1 25 . 1 V ADJ OUT R R R V ¸ ¹ · ¨ © § Copyright © 2017, Texas Instruments Incorporated 13 LM138QML www.ti.com SNVSAA9 – OCTOBER 2017 Product Folder Links: LM138QML Submit Documentation Feedback Copyright © 2017, Texas Instruments Incorporated 8.2 Typical Applications 8.2.1 Constant 5-V Regulator Figure 15. Constant 5-V Regulator 8.2.1.1 Design Requirements Table 1. Design Parameters PARAMETER PART NUMBER/VALUE DESCRIPTION Feedback resistor 1 (R1) 270 Ω The LM138QML produces a typical 1.24-V potential between the OUTPUT and ADJUST pins; therefore, placing a 270-Ω resistor between the OUTPUT and ADJUST pins causes 4.6 mA to flow through R1 and R2 Feedback resistor 2 (R2) 820 Ω To achieve a 5-V output, the sum of the voltages across R1 and R2 must equal 5 V. Therefore, VR2 must equal 3.76 V when 4.6 mA is flowing through it. R2 = VR2 / I = 3.76 V / 4.6 mA = ~820 Ω. Input capacitor (CIN) 0.1 µF 0.1 µF of input capacitance helps filter out unwanted noise, especially if the regulator is located far from the power supply filter capacitors. Output capacitor (COUT) 1 µF The regulator is stable without any output capacitance, but adding a 1-µF capacitor improves the transient response. Adjust capacitor (CADJ) 10 µF A 10-µF capacitor bypassing the ADJUST pin to ground improves the regulators ripple rejection. Protection diode 1 (D1) 1N4002 Protection diode D1 is recommended if COUT is used. The diode provides a low- impedance discharge path to prevent the capacitor from discharging into the output of the regulator (see Protection Diodes). Protection diode 2 (D2) 1N4002 Protection diode D2 is recommended if CADJ is used. The diode provides a low-impedance discharge path to prevent the capacitor from discharging into the output of the regulator (see Protection Diodes). |
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