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RT9164A-35GLR Datasheet(PDF) 10 Page - Richtek Technology Corporation |
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RT9164A-35GLR Datasheet(HTML) 10 Page - Richtek Technology Corporation |
10 / 14 page RT9164A 10 DS9164A-13 August 2007 www.richtek.com Application Information Output voltage adjustment Like most regulators, the RT9164A regulates the output by comparing the output voltage to an internally generated reference voltage. On the adjustable version as shown in Figure 4, the VREF is available externally as 1.25V between VOUT and ADJ. The voltage ratio formed by R1 and R2 should be set to conduct 10mA (minimum output load). The output voltage is given by the following equation: VOUT = VREF (1+ 1 2 R R ) + IADJ R2 On fixed versions of RT9164A, the voltage divider is provided internally. Figure 4. Basic Adjustable Regulator Input Bypass Capacitor An input capacitor is recommended. A 10 μF tantalum on the input is a suitable input bypassing for almost all applications. Adjust Terminal Bypass Capacitor The adjust terminal can be bypassed to ground with a bypass capacitor (CADJ) to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. At any ripple frequency, the impedance of the CADJ should be less than R1 to prevent the ripple from being amplified: (2 π x fRIPPLE x CADJ) < R1 The R1 is the resistor between the output and the adjust pin. Its value is normally in the range of 100-200 Ω. For example, with R1 = 124 Ω and fRIPPLE = 120Hz, the CADJ should be > 11 μF. Output Capacitor RT9164A requires a capacitor from VOUT to GND to provide compensation feedback to the internal gain stage. This is to ensure stability at the output terminal. Typically, 10 μF tantalum or 50 μF aluminum electrolytic with 30mΩ to 2Ω range capacitor is sufficient. The output capacitor does not have a theoretical upper limit and increasing its value will increase stability. COUT = 100 μF or more is typical for high current regulator design. VIN VOUT ADJ RT9164A R1 R2 10uF 10uF I ADJ V REF V IN V OUT 65uF C ADJ C IN C OUT Load Regulation When the adjustable regulator is used (Figure 6), the best load regulation is accomplished when the top of the resistor divider (R1) is connected directly to the output pin of the RT9164A. When so connected, RP is not multiplied by the divider ratio. For Fixed output version, the top of R1 is internally connected to the output and ground pins can be connected to low side of the load. Figure 5 Region of Stable COUT ESR vs. Load Current 0.01 0.1 1 10 0 0.2 0.4 0.6 0.8 1 Load Current (A) COUT = 100uF COUT = 10uF Instable Instable Stable |
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