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RT9170-32GV Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9170-32GV Datasheet(HTML) 8 Page - Richtek Technology Corporation |
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8 / 13 page  RT9170 8 DS9170-11 March 2007 www.richtek.com Application Information Like any low-dropout regulator, the RT9170 requires input and output decoupling capacitors. The device is specifically designed for portable applications requiring minimum board space and smallest components. 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 1 μF 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 1 μF over the entire operating temperature range. Output Capacitor The RT9170 is designed specifically to work with very small ceramic output capacitors. A ceramic capacitor (temperature characteristics X7R, X5R, Z5U, or Y5V) in 1 μF to 10μF with 5mΩ to 50mΩ range is suitable for the RT9170 application. The recommended minimum capacitance for the device is 1 μF, X5R or X7R dielectric ceramic, between VOUT and GND for 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. No Load Stability The device will remain stable and in regulation with no external load. This is specially import in CMOS RAM keep- alive applications. Input-Output (Dropout) Volatge A regulator's minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Because the device uses a PMOS, its dropout voltage is a function of drain-to- source on-resistance, RDS(ON), multiplied by the load current : VDROPOUT = VIN -VOUT = RDS(ON) x IOUT Current Limit The RT9170 monitors and controls the PMOS' gate voltage, limiting the output current to 0.3A (min). The output can be shorted to ground for an indefinite period of time without damaging the part. Short-Circuit Protection The device is short circuit protected and in the event of a peak over-current condition, the short-circuit control loop will rapidly drive the output PMOS pass element off. Once the power pass element shuts down, the control loop will rapidly cycle the output on and off until the average power dissipation causes the thermal shutdown circuit to respond to servo the on/off cycling to a lower frequency. Please refer to the section on thermal information for power dissipation calculations. Capacitor Characteristics It is important to note that capacitance tolerance and variation with temperature must be taken into consideration when selecting a capacitor so that the minimum required amount of capacitance is provided over the full operating temperature range. In general, a good tantalum capacitor will show very little capacitance variation with temperature, but a ceramic may not be as good (depending on dielectric type). ≅ ≅ |
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