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RT9178-32PB Datasheet(PDF) 7 Page - Richtek Technology Corporation |
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RT9178-32PB Datasheet(HTML) 7 Page - Richtek Technology Corporation |
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7 / 11 page  RT9178 7 DS9178-16 April 2008 www.richtek.com Application Information The RT9178 is ideal for mobile phone and similar battery- powered wireless applications. It provides up to 200mA, from a 2.5V to 6V input. Like any low-dropout regulator, the device requires input and output decoupling capacitors. These capacitors must be correctly selected for good performance (see Capacitor Characteristics Section). Please note that linear regulators with a low dropout voltage have high internal loop gains which require care in guarding against oscillation caused by insufficient decoupling capacitance. Input Capacitor An input capacitance of ≅1μF is required between the device input pin and ground directly (the amount of the capacitance may be increased without limit). The input capacitor MUST be located less than 1 cm from the device to assure input stability (see PCB Layout Section). A lower ESR capacitor allows the use of less capacitance, while higher ESR type (like aluminum electrolytic) require more capacitance. Capacitor types (aluminum, ceramic and tantalum) can be mixed in parallel, but the total equivalent input capacitance/ESR must be defined as above to stable operation. There are no requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will be ≅1μF over the entire operating temperature range. Output Capacitor The RT9178 is designed specifically to work with very small ceramic output capacitors. The recommended minimum capacitance (temperature characteristics X7R, X5R, Z5U or Y5V) is 1 μF to 10μF range with 5mΩ to 50m Ω range ceramic capacitor between LDO output and GND for transient stability, but it may be increased without limit. Higher capacitance values help to improve transient. The output capacitor's ESR is critical because it forms a zero to provide phase lead which is required for loop stability. Reference Bypass Capacitor (BP) Connecting a 10nF between the BP (reference bypass) pin and GND significantly reduces noise on the regulator output. It should be noted that the capacitor is connected directly to a high impedance circuit in the band gap reference. Because this circuit has only a few micro- amperes flowing into it, any significantly loading on this node will cause a change on the regulated output voltage. For this reason, DC leakage current through the noise bypass capacitor must never exceed 100nA, and should be kept as low as possible for best output voltage accuracy. The type of capacitors best suited for the noise bypass capacitor with either NP0 or C0G dielectric typically have very low leakage. 10nF polypropylene and polycarbonate film capacitors are available in small surface mount packages and typically have extremely low leakage current. No Load Stability The device will remain stable and in regulation with no external load. This is specially important in CMOS RAM keep-alive applications Shutdown Input Operation The RT9178 is shutdown by pulling the EN pin low, and turned on by driving the input high. If the shutdown feature is not required, the EN pin should be tied to VIN to keep the regulator on at all times (the EN pin MUST NOT be left floating). Region of Stable COUT ESR vs. Load Current 0.00 0.01 0.10 1.00 10.00 100.00 0 40 80 120 160 200 Load Current (mA) 100 10 Unstable Unstable Stable |
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Similar Description - RT9178-32PB |
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